Release v172 (#995)

Bumps [rake](https://github.com/ruby/rake) from 12.3.1 to 12.3.3.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](https://github.com/ruby/rake/compare/v12.3.1...v12.3.3)

.dockerignore

@@ -0,0 +1 @@
+.git/

.github/CODEOWNERS

@@ -0,0 +1 @@
+* @heroku/languages

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,8 @@
+<!-- Hi and welcome to the Heroku Python buildpack repository!
+
+If you meant to open a PR against a fork instead of upstream, please adjust the base branch:
+https://help.github.com/articles/changing-the-base-branch-of-a-pull-request/
+
+Otherwise thank you in advance for your Pull Request - just remember to
+include as much information as possible to help the reviewers :-)
+-->

.github/workflows/check_changelog.yml

@@ -0,0 +1,14 @@
+name: Check Changelog
+
+on:
+ pull_request:
+  types: [opened, reopened, edited, synchronize]
+
+jobs:
+ build:
+   runs-on: ubuntu-latest
+   steps:
+   - uses: actions/checkout@v1
+   - name: Check that CHANGELOG is touched
+     run: |
+       cat $GITHUB_EVENT_PATH | jq .pull_request.title |  grep -i '\[\(\(changelog skip\)\|\(ci skip\)\)\]' ||  git diff remotes/origin/${{ github.base_ref }} --name-only | grep CHANGELOG.md

.gitignore

@@ -1,3 +1,14 @@
 *.pyc
 site
 .DS_Store
+
+/.envrc
+repos/*
+
+#Venv
+buildpack/*
+
+builds/dockerenv.staging*
+builds/dockerenv.production
+
+test/scratch

.pre-commit-config.yaml

@@ -0,0 +1,7 @@
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.3.0
+    hooks:
+    -   id: check-yaml
+    -   id: end-of-file-fixer
+    -   id: trailing-whitespace

.travis.yml

@@ -1,9 +1,44 @@
-language: bash
+language: ruby
+dist: bionic
 sudo: required
-services:
-  - docker
-# install: docker pull heroku/cedar:14
-script: ./tests.sh
+branches:
+  only:
+  - master
+
+rvm:
+- 2.6.6
+before_script:
+  - gem install bundler -v 1.16.2
+
+script:
+  - docker build --pull --tag travis-build-cedar-14 --file $(pwd)/builds/cedar-14.Dockerfile .
+  - docker run --rm -e "STACK=cedar-14" travis-build-cedar-14 bash $TESTFOLDER
+  - docker build --pull --tag travis-build-heroku-16 --file $(pwd)/builds/heroku-16.Dockerfile .
+  - docker run --rm -e "STACK=heroku-16" travis-build-heroku-16 bash $TESTFOLDER
+  - docker build --pull --tag travis-build-heroku-18 --file $(pwd)/builds/heroku-18.Dockerfile .
+  - docker run --rm -e "STACK=heroku-18" travis-build-heroku-18 bash $TESTFOLDER
+
+jobs:
+  include:
+  - stage: Bash linting (shellcheck)
+    sudo: false
+    script: make check
+  - stage: Hatchet Integration
+    if: env(TRAVIS_PULL_REQUEST_SLUG) = env(TRAVIS_REPO_SLUG)
+    name: Run Hatchet
+    script:
+      - bundle exec hatchet ci:setup
+      - PARALLEL_SPLIT_TEST_PROCESSES=11 bundle exec parallel_split_test spec/hatchet/
+
 env:
-  - STACK=heroku-16
-  - STACK=cedar-14
+  matrix:
+    - TESTFOLDER=test/run-deps
+    - TESTFOLDER=test/run-versions
+    - TESTFOLDER=test/run-features
+  global:
+    - HATCHET_RETRIES=3
+    - IS_RUNNING_ON_CI=true
+    - HATCHET_APP_LIMIT=80
+    - HATCHET_DEPLOY_STRATEGY=git
+    - secure: yjtlPE5FbVxTKnjUy/tZUBgSEf4qADD3QOxtgziuid73S0U/1IEXlMGFULsQzIjtlHKmHeywZqpVVEpthIH4RuT7uoX1Pb7SSM/g0T8fT3VoEFbFK1uYl0oZQbUS4Klxv9tPiumj8if3m6ULEGIz1X0wZcMOC0tMLwVCnwmap0E=
+    - secure: ZeFTHWwnpIKE9nAqs88ocmiQh7bKce84lilGm5J23nf3N6V4wNyLwqlkvsM008WGBCaOg9AUx7ZunasT0ANsR5gLP3eV2UUg7ILdRgV2Gy13eNRFheC4PHdN92RqQ3aKoqlIv2K999xlhVjod0NzhkQQXB6PddfQINbuU7ks6As=

CHANGELOG.md

@@ -1,5 +1,343 @@
 # Python Buildpack Changelog
 
+# Master
+
+
+# 172 (2020-07-17)
+
+- Python 3.8.4 is now available (CPython)
+
+# 171 (2020-07-07)
+
+- Python 3.6.11 and 3.7.8 are now available (CPython).
+
+# 170 (2020-05-19)
+
+- Python 2.7.18, 3.5.9, 3.7.7 and 3.8.3 are now available (CPython).
+- PyPy 2.7 and 3.6, version 7.3.1 are now available (Note: PyPy support is in beta)
+- Docs: Fix explanation of runtime.txt generation when using pipenv
+- Bugfix: Correctly detect Python version when using a `python_version` of `3.8` in `Pipfile.lock`
+
+--------------------------------------------------------------------------------
+
+# 169 (2020-04-22)
+
+- Add a Hatchet test for python 3.8.2
+- Set Code Owners to @heroku/langauges
+- Bugfix: Caching on subsequent redeploys
+- Update tests to support latest version of Python
+
+# 168 (2020-04-06)
+
+- Doc: Update Readme with version numbers
+- update Code Owners to include the Heroku Buildpack Maintainers team
+- Deprecation warning: BUILD_WITH_GEO_LIBRARIES is now deprecated. See warning for details.
+- Clean up build log output
+- Update Python versions in README to match docs
+- Django version detection fixed, link updated
+
+# 167 (2020-03-26)
+
+- Add failcase for cache busting
+- Bugfix: Clearing pip dependencies
+
+# 166 (2020-03-05)
+
+- Correct ftp to https in vendored file
+- Warn for Django 1.11 approaching EOL, provide link to roadmap
+
+# 165 (2020-02-27)
+
+- Python 3.8.2 now available.
+
+# 164 (2020-02-20)
+
+- Update requirements.txt builds to use Pip 20.0.2
+- Download get-pip.py to tmpdir instead of root dir
+
+# 163 (2019-12-23)
+
+- New pythons released:
+  Python 3.8.1, 3.7.6, 3.6.10 (CPython)
+  Beta Release: Pypy 2.7 and 3.6, version 7.2.0
+
+# 162 (2019-12-06)
+
+- Bug fix: fragile sqlite3 install
+
+# 161 (2019-12-2)
+
+- Bug fix: Sqlite3 version bump
+
+# 160 (2019-10-23)
+
+- Bugfix: Pipenv no longer installs twice in CI
+
+# 159 (2019-10-22)
+
+- Python 2.7.17 now available on Heroku 18 and 16.
+
+# 158 (2019-10-21)
+
+- Python 3.7.5 and 3.8.0 now available on Heroku 18 and 16.
+- Add support for Python 3.8 branch
+- Sqlite3 Update:
+  - Test Improvements
+- Add support for staging binary testing
+
+# 157 (2019-09-18)
+
+- Typo fixes
+
+# 156 (2019-09-12)
+
+- Python 3.6.9 and 3.7.4 now available.
+
+- Move get-pip utility to S3
+- Build utility and documentation updates
+- Bump Hatchet tests to point at new default python version.
+
+# 155 (2019-08-22)
+
+add docs and make target for heroku-18 bob builds
+
+# 154 (2019-07-17)
+
+Fix python 3.5.7 formula actually building 3.7.2
+
+# 153 (2019-06-21)
+
+Hotfix for broken heroku-16 deploys
+
+# 152 (2019-04-04)
+
+Python 3.7.3 now available.
+
+# 151 (2019-03-21)
+
+Python 3.5.7 and 3.4.10 now available on all Heroku stacks.
+
+# 150 (2019-03-13)
+
+Python 2.7.16 now available on all Heroku stacks.
+
+# 149 (2019-03-04)
+
+Hotfix for broken Cedar 14 deploys
+
+# 148 (2019-02-21)
+
+No user facing changes, improving internal metrics
+
+# 147 (2019-02-07)
+
+Python 3.7.2 and 3.6.8 now available on all Heroku stacks.
+
+# 146 (2018-11-11)
+
+Python 3.7.1, 3.6.7, 3.5.6 and 3.4.9 now available on all Heroku stacks.
+
+# 145 (2018-11-08)
+
+Testing and tooling expanded to better support new runtimes
+
+# 144 (2018-10-10)
+
+Switch to cautious upgrade for Pipenv install to ensure the pinned pip version
+is used with Pipenv
+
+# 143 (2018-10-09)
+
+Add support for detecting SLUGIFY_USES_TEXT_UNIDECODE, which is required to
+install Apache Airflow version 1.10 or higher.
+
+# 142 (2018-10-08)
+
+Improvements to Python install messaging
+
+# 139, 140, 141
+
+No user-facing changes, documenting for version clarity
+
+# 138 (2018-08-01)
+
+Use stack image SQLite3 instead of vendoring
+
+# 137 (2018-07-17)
+
+Prevent 3.7.0 from appearing as unsupported in buildpack messaging.
+
+# 136 (2018-06-28)
+
+Upgrade to 3.6.6 and support 3.7.0 on all runtimes.
+
+# 135 (2018-05-29)
+
+Upgrade Pipenv to v2018.5.18.
+
+# 134 (2018-05-02)
+
+Default to 3.6.5, bugfixes.
+
+# 133
+
+Fixes for Pip 10 release.
+
+# 132
+
+Improve pip installation, with the release of v9.0.2.
+
+# 131
+
+Fix bug with pip.
+
+# 130
+
+Better upgrade strategy for pip.
+
+# 129
+
+Don't upgrade pip (from v128).
+
+# 128
+
+Upgrade pip, pin to Pipenv v11.8.2.
+
+# 127
+
+Pin to Pipenv v11.7.1.
+
+# 126
+
+Bugfixes.
+
+# 125
+
+Bugfixes.
+
+# 124
+
+Update buildpack to automatically install `[dev-packages]` during Heroku CI Pipenv builds.
+
+- Skip installs if Pipfile.lock hasn't changed, and uninstall stale dependencies with Pipenv.
+- Set `PYTHONPATH` during collectstatic runs.
+- No longer warn if there is no `Procfile`.
+- Update Pipenv's "3.6" runtime specifier to point to "3.6.4".
+
+# 123
+
+Update gunicorn `init.d` script to allow overrides.
+
+# 122
+
+Update default Python to v3.6.4.
+
+# 121
+
+Update default Python to v3.6.3.
+
+# 120
+
+Use `$ pipenv --deploy`.
+
+# 119
+
+Improvements to Pipenv support, warning on unsupported Python versions.
+
+- We now warn when a user is not using latest 2.x or 3.x Python.
+- Heroku now supports `[requires]` `python_full_version` in addition to `python_version`.
+
+# 118
+
+Improvements to Pipenv support.
+
+# 117
+
+Bug fix.
+
+# 116
+
+Vendoring improvements.
+
+- Geos libraries should work on Heroku-16 now.
+- The libffi/libmemcached vendoring step is now skipped on Heroku-16 (since they are installed in the base image).
+
+# 115
+
+Revert a pull request.
+
+- No longer using `sub_env` for `pip install` step.
+
+# 114
+
+- Bugfixes.
+
+Blacklisting `PYTHONHOME` and `PYTHONPATH` for older apps. Upgrades to nltk support.
+
+# 113
+
+Updates to Pipenv support.
+
+# 112
+
+Bugfix.
+
+- Fixed grep output bug.
+
+# 111
+
+Linting, bugfixes.
+
+# 110
+
+Update default Python to 3.6.2.
+
+# 109
+
+Update Default Python to 3.6.1, bugfixes.
+
+- Fixed automatic pip uninstall of dependencies removed from requirements.txt.
+
+# 108
+
+Fix output for collectstatic step.
+
+# 107
+
+Bugfix for C dependency installation.
+
+# 106
+
+ Don't install packages that could mess up packaging.
+
+ - The Python buildpack will automatically remove `six`, `pyparsing`, `appdirs`,
+   `setuptools`, and `distribute` from a `requirements.txt` file now, as these
+   packages are provided by the Python buildpack.
+
+ # 105
+
+ Improvements to output messaging.
+
+# 104
+
+General improvements.
+
+- Fix for Heroku CI.
+- Use `pkg_resources` to check if a distribution is installed instead of
+  parsing `requirements.txt`. ([#395][395])
+
+[395]: https://github.com/heroku/heroku-buildpack-python/pull/395
+
+## 103
+
+Bug fixes and improvements.
+
+- Fix for Pipenv.
+- Fix for Heroku CI.
+- Improve handling of WEB_CONCURRENCY when using multiple buildpacks.
+- Adjust environment variables set during the build to more closely match those in the dyno environment (DYNO is now available, STACK is not).
+- Restore the build cache prior to running bin/pre_compile.
+
 ## 102
 
 Buildpack code cleanup.

Dockerfile

@@ -1,11 +0,0 @@
-FROM heroku/heroku:16-build
-
-WORKDIR /app
-ENV WORKSPACE_DIR=/app/builds
-
-RUN apt-get update && apt-get install -y python-pip
-
-# Install bob-builder application
-RUN pip install bob-builder==0.0.5
-
-COPY . /app

Gemfile

@@ -0,0 +1,8 @@
+source "https://rubygems.org"
+
+gem "rspec"
+gem "heroku_hatchet"
+gem "rspec-retry"
+gem "rake"
+gem "parallel_split_test"
+

Gemfile.lock

@@ -0,0 +1,78 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (6.0.3.1)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      i18n (>= 0.7, < 2)
+      minitest (~> 5.1)
+      tzinfo (~> 1.1)
+      zeitwerk (~> 2.2, >= 2.2.2)
+    concurrent-ruby (1.1.6)
+    diff-lcs (1.3)
+    erubis (2.7.0)
+    excon (0.73.0)
+    heroics (0.0.25)
+      erubis (~> 2.0)
+      excon
+      moneta
+      multi_json (>= 1.9.2)
+    heroku_hatchet (5.0.3)
+      excon (~> 0)
+      minitest-retry (~> 0.1.9)
+      platform-api (~> 2)
+      repl_runner (~> 0.0.3)
+      rrrretry (~> 1)
+      thor (~> 0)
+      threaded (~> 0)
+    i18n (1.8.2)
+      concurrent-ruby (~> 1.0)
+    minitest (5.14.1)
+    minitest-retry (0.1.9)
+      minitest (>= 5.0)
+    moneta (1.0.0)
+    multi_json (1.14.1)
+    parallel (1.19.1)
+    parallel_split_test (0.7.0)
+      parallel (>= 0.5.13)
+      rspec (>= 3.1.0)
+    platform-api (2.2.0)
+      heroics (~> 0.0.25)
+      moneta (~> 1.0.0)
+    rake (12.3.3)
+    repl_runner (0.0.3)
+      activesupport
+    rrrretry (1.0.0)
+    rspec (3.8.0)
+      rspec-core (~> 3.8.0)
+      rspec-expectations (~> 3.8.0)
+      rspec-mocks (~> 3.8.0)
+    rspec-core (3.8.0)
+      rspec-support (~> 3.8.0)
+    rspec-expectations (3.8.1)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-mocks (3.8.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-retry (0.6.1)
+      rspec-core (> 3.3)
+    rspec-support (3.8.0)
+    thor (0.20.3)
+    thread_safe (0.3.6)
+    threaded (0.0.4)
+    tzinfo (1.2.7)
+      thread_safe (~> 0.1)
+    zeitwerk (2.3.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  heroku_hatchet
+  parallel_split_test
+  rake
+  rspec
+  rspec-retry
+
+BUNDLED WITH
+   2.1.4

LICENSE

@@ -1,6 +1,6 @@
 MIT License:
 
-Copyright (C) 2016 Heroku, Inc.
+Copyright (C) 2017 Heroku, Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 

Makefile

@@ -1,19 +1,55 @@
 # These targets are not files
 .PHONY: tests
 
-test: test-cedar-14
+test: test-heroku-18 test-heroku-16 test-cedar-14
+
+check:
+	@shellcheck -x bin/compile bin/detect bin/release bin/test-compile bin/utils bin/warnings bin/default_pythons
+	@shellcheck -x bin/steps/collectstatic bin/steps/eggpath-fix  bin/steps/eggpath-fix2 bin/steps/gdal bin/steps/geo-libs bin/steps/mercurial bin/steps/nltk bin/steps/pip-install bin/steps/pip-uninstall bin/steps/pipenv bin/steps/pipenv-python-version bin/steps/pylibmc bin/steps/python
+	@shellcheck -x bin/steps/hooks/*
 
 test-cedar-14:
 	@echo "Running tests in docker (cedar-14)..."
-	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=cedar-14" heroku/cedar:14 bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'
+	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=cedar-14" heroku/cedar:14 bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run-deps; test/run-features; test/run-versions;'
 	@echo ""
 
 test-heroku-16:
 	@echo "Running tests in docker (heroku-16)..."
-	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-16" heroku/heroku:16-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'
+	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-16" heroku/heroku:16-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run-deps; test/run-features; test/run-versions;'
 	@echo ""
 
+test-heroku-18:
+	@echo "Running tests in docker (heroku-18)..."
+	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-18" heroku/heroku:18-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run-deps; test/run-features; test/run-versions;'
+	@echo ""
+
+buildenv-heroku-16:
+	@echo "Creating build environment (heroku-16)..."
+	@echo
+	@docker build --pull -f $(shell pwd)/builds/heroku-16.Dockerfile -t python-buildenv-heroku-16 .
+	@echo
+	@echo "Usage..."
+	@echo
+	@echo "  $$ export AWS_ACCESS_KEY_ID=foo AWS_SECRET_ACCESS_KEY=bar  # Optional unless deploying"
+	@echo "  $$ bob build runtimes/python-2.7.13"
+	@echo "  $$ bob deploy runtimes/python-2.7.13"
+	@echo
+	@docker run -it --rm python-buildenv-heroku-16
+
+buildenv-heroku-18:
+	@echo "Creating build environment (heroku-18)..."
+	@echo
+	@docker build --pull -f $(shell pwd)/builds/heroku-18.Dockerfile -t python-buildenv-heroku-18 .
+	@echo
+	@echo "Usage..."
+	@echo
+	@echo "  $$ export AWS_ACCESS_KEY_ID=foo AWS_SECRET_ACCESS_KEY=bar  # Optional unless deploying"
+	@echo "  $$ bob build runtimes/python-2.7.13"
+	@echo "  $$ bob deploy runtimes/python-2.7.13"
+	@echo
+	@docker run -it --rm python-buildenv-heroku-18
+
 tools:
 	git clone https://github.com/kennethreitz/pip-pop.git
 	mv pip-pop/bin/* vendor/pip-pop/
-	rm -fr pip-pop
+	rm -fr pip-pop

README.md

@@ -4,38 +4,55 @@
 
 [![Build Status](https://travis-ci.org/heroku/heroku-buildpack-python.svg?branch=master)](https://travis-ci.org/heroku/heroku-buildpack-python)
 
-This is the official [Heroku buildpack](https://devcenter.heroku.com/articles/buildpacks) for Python apps, powered by [pip](https://pip.pypa.io/) and other excellent software.
+This is the official [Heroku buildpack](https://devcenter.heroku.com/articles/buildpacks) for Python apps.
 
-Recommended web frameworks include **Django** and **Flask**. The recommended webserver is **Gunicorn**. There are no restrictions around what software can be used (as long as it's pip-installable). Web processes must bind to `$PORT`, and only the HTTP protocol is permitted for incoming connections.
+Recommended web frameworks include **Django** and **Flask**, among others. The recommended webserver is **Gunicorn**. There are no restrictions around what software can be used (as long as it's pip-installable). Web processes must bind to `$PORT`, and only the HTTP protocol is permitted for incoming connections.
 
-Some Python packages with obscure C dependencies (e.g. scipy) are [not compatible](https://devcenter.heroku.com/articles/python-c-deps). 
+Python packages with C dependencies that are not [available on the stack image](https://devcenter.heroku.com/articles/stack-packages) are generally not supported, unless `manylinux` wheels are provided by the package maintainers (common). For recommended solutions, check out [this article](https://devcenter.heroku.com/articles/python-c-deps) for more information.
 
 See it in Action
 ----------------
+```
+$ ls
+my-application		requirements.txt	runtime.txt
 
-Deploying a Python application couldn't be easier:
+$ git push heroku master
+Counting objects: 4, done.
+Delta compression using up to 8 threads.
+Compressing objects: 100% (2/2), done.
+Writing objects: 100% (4/4), 276 bytes | 276.00 KiB/s, done.
+Total 4 (delta 0), reused 0 (delta 0)
+remote: Compressing source files... done.
+remote: Building source:
+remote:
+remote: -----> Python app detected
+remote: -----> Installing python-3.7.4
+remote: -----> Installing pip
+remote: -----> Installing SQLite3
+remote: -----> Installing requirements with pip
+remote:        Collecting flask (from -r /tmp/build_c2c067ef79ff14c9bf1aed6796f9ed1f/requirements.txt (line 1))
+remote:          Downloading ...
+remote:        Installing collected packages: Werkzeug, click, MarkupSafe, Jinja2, itsdangerous, flask
+remote:        Successfully installed Jinja2-2.10 MarkupSafe-1.1.0 Werkzeug-0.14.1 click-7.0 flask-1.0.2 itsdangerous-1.1.0
+remote:
+remote: -----> Discovering process types
+remote:        Procfile declares types -> (none)
+remote:
+```
 
-    $ ls
-    Procfile  requirements.txt  web.py
+A `requirements.txt` must be present at the root of your application's repository to deploy.
 
-    $ heroku create --buildpack heroku/python
+To specify your python version, you also need a `runtime.txt` file - unless you are using the default Python runtime version.
 
-    $ git push heroku master
-    ...
-    -----> Python app detected
-    -----> Installing python-2.7.13
-         $ pip install -r requirements.txt
-           Collecting requests (from -r requirements.txt (line 1))
-             Downloading requests-2.12.4-py2.py3-none-any.whl (576KB)
-           Installing collected packages: requests
-           Successfully installed requests-2.12.4
-           
-    -----> Discovering process types
-           Procfile declares types -> (none)
+Current default Python Runtime: Python 3.6.9
 
-A `requirements.txt` file must be present at the root of your application's repository.
+Alternatively, you can provide a `setup.py` file, or a `Pipfile`.
+Using `pipenv` will generate `runtime.txt` at build time if one of the field `python_version` or `python_full_version` is specified in the `requires` section of your `Pipfile`.
 
-You can also specify the latest production release of this buildpack for upcoming builds of an existing application:
+Specify a Buildpack Version
+---------------------------
+
+You can specify the latest production release of this buildpack for upcoming builds of an existing application:
 
     $ heroku buildpacks:set heroku/python
 
@@ -43,14 +60,31 @@ You can also specify the latest production release of this buildpack for upcomin
 Specify a Python Runtime
 ------------------------
 
-Specific versions of the Python runtime can be specified with a `runtime.txt` file:
+Supported runtime options include:
 
-    $ cat runtime.txt
-    python-3.6.0
+- `python-3.8.4`
+- `python-3.7.8`
+- `python-3.6.11`
+- `python-2.7.18`
 
-Runtime options include:
+## Tests
 
-- `python-2.7.13`
-- `python-3.6.0`
-- `pypy-5.6.0` (unsupported, experimental)
-- `pypy3-5.5.0` (unsupported, experimental)
+The buildpack tests use [Docker](https://www.docker.com/) to simulate
+Heroku's [stack images.](https://devcenter.heroku.com/articles/stack)
+
+To run the test suite:
+
+```
+make test
+```
+
+Or to test in a particular stack:
+
+```
+make test-heroku-18
+make test-heroku-16
+```
+
+The tests are run via the vendored
+[shunit2](https://github.com/kward/shunit2)
+test framework.

Rakefile

@@ -0,0 +1 @@
+require 'hatchet/tasks'

bin/compile

@@ -15,207 +15,386 @@
 # Fail fast and fail hard.
 set -eo pipefail
 
+# Boostrap the Buildpack Standard Library.
+export BPLOG_PREFIX="buildpack.python"
+export BUILDPACK_LOG_FILE=${BUILDPACK_LOG_FILE:-/dev/null}
+
 [ "$BUILDPACK_XTRACE" ] && set -o xtrace
 
-# Prepend proper path for virtualenv hackery. This will be deprecated soon.
+# Prepend proper path for old-school virtualenv hackery.
+# This may not be neccessary.
 export PATH=:/usr/local/bin:$PATH
 
-# Paths.
-BIN_DIR=$(cd $(dirname $0); pwd) # absolute path
-ROOT_DIR=$(dirname $BIN_DIR)
+# Setup Path variables, for later use in the Buildpack.
+BIN_DIR=$(cd "$(dirname "$0")"; pwd) # absolute path
+ROOT_DIR=$(dirname "$BIN_DIR")
 BUILD_DIR=$1
 CACHE_DIR=$2
 ENV_DIR=$3
 
-# Python defaults
-DEFAULT_PYTHON_VERSION="python-2.7.13"
-DEFAULT_PYTHON_STACK="cedar-14"
-PYTHON_EXE="/app/.heroku/python/bin/python"
-PIP_VERSION="9.0.1"
-SETUPTOOLS_VERSION="32.1.0"
+# Export Path variables, for use in sub-scripts.
+export BUILD_DIR CACHE_DIR ENV_DIR
 
-# Common Problem Warnings
-export WARNINGS_LOG=$(mktemp)
+# Set the Buildpack's internet target for downloading Python distributions.
+# The user can provide BUILDPACK_VENDOR_URL to specify a custom target.
+# Note: this is designed for non-Heroku use, as it does not use the user-provided
+# environment variable mechanism (the ENV_DIR).
+VENDOR_URL="https://lang-python.s3.amazonaws.com/$STACK"
+if [[ -n ${BUILDPACK_VENDOR_URL:-} ]]; then
+    VENDOR_URL="$BUILDPACK_VENDOR_URL"
+elif [[ -n ${USE_STAGING_BINARIES} ]]; then
+    VENDOR_URL="$USE_STAGING_BINARIES/$STACK"
+fi
+export VENDOR_URL
+
+# Default Python Versions
+# shellcheck source=bin/default_pythons
+source "$BIN_DIR/default_pythons"
+
+# Supported Python Branches
+PY38="python-3.8"
+PY37="python-3.7"
+PY36="python-3.6"
+PY35="python-3.5"
+PY34="python-3.4"
+PY27="python-2.7"
+PYPY27="pypy2.7"
+PYPY36="pypy3.6"
+
+# Which stack is used (for binary downloading), if none is provided (e.g. outside of Heroku)?
+DEFAULT_PYTHON_STACK="cedar-14"
+# If pip doesn't match this version (the version we install), run the installer.
+PIP_UPDATE="20.0.2"
+
+for file in "$BUILD_DIR/runtime.txt" "$CACHE_DIR/.heroku/python-version" ; do
+    [ -f "$file" ] || continue
+
+    version=$(tr -d '[:space:]' < "$file")
+
+    case "$version" in "$PY34"*)
+        # Python 3.4 support was dropped in pip >= 19.2.
+        PIP_UPDATE="19.1.1"
+        break
+        ;;
+    esac
+done
+
+if [[ -f "$BUILD_DIR/Pipfile" ]]; then
+    # Do not force pipenv users to re-install pipenv locally.
+    PIP_UPDATE="9.0.2"
+fi
+
+export DEFAULT_PYTHON_STACK PIP_UPDATE
+export PY37 PY36 PY35 PY27 PY34
+
+# Common Problem Warnings:
+# This section creates a temporary file in which to stick the output of `pip install`.
+# The `warnings` subscript then greps through this for common problems and guides
+# the user towards resolution of known issues.
+WARNINGS_LOG=$(mktemp)
+export WARNINGS_LOG
 export RECOMMENDED_PYTHON_VERSION=$DEFAULT_PYTHON_VERSION
 
-# Setup vendored tools and pip-pop (pip-diff)
+# The buildpack ships with a few executable tools (e.g. pip-grep, etc).
+# This installs them into the path, so we can execute them directly.
 export PATH=$PATH:$ROOT_DIR/vendor/:$ROOT_DIR/vendor/pip-pop
 
-# Support Anvil Build_IDs
+# Set environment variables if they weren't set by the platform.
+# Note: this is legacy, for a deprecated build system known as Anvil.
+# This can likely be removed, with caution.
 [ ! "$SLUG_ID" ] && SLUG_ID="defaultslug"
 [ ! "$REQUEST_ID" ] && REQUEST_ID=$SLUG_ID
 [ ! "$STACK" ] && STACK=$DEFAULT_PYTHON_STACK
 
-# Sanitizing environment variables.
+# Sanitize externally-provided environment variables:
+# The following environment variables are either problematic or simply unneccessary
+# for the buildpack to have knowledge of, so we unset them, to keep the environment
+# as clean and pristine as possible.
 unset GIT_DIR PYTHONHOME PYTHONPATH
-unset RECEIVE_DATA RUN_KEY BUILD_INFO DEPLOY LOG_TOKEN DYNO
+unset RECEIVE_DATA RUN_KEY BUILD_INFO DEPLOY LOG_TOKEN
 unset CYTOKINE_LOG_FILE GEM_PATH
 
-# Syntax sugar.
-source $BIN_DIR/utils
+# Import the utils script, which contains helper functions used throughout the buildpack.
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
-# Import collection of warnings.
-source $BIN_DIR/warnings
+# Import the warnings script, which contains the `pip install` user warning mechanisms
+# (mentioned and explained above)
+# shellcheck source=bin/warnings
+source "$BIN_DIR/warnings"
 
-# we need to put a bunch of symlinks in there later
+# Make the directory in which we will create symlinks from the temporary build directory
+# to `/app`.
+# Symlinks are required, since Python is not a portable installation.
+# More on this topic later.
 mkdir -p /app/.heroku
 
-# Set up outputs under new context
+# This buildpack programatically generates (or simply copies) a number of files for
+# buildpack machinery: an export script, and a number of `.profile.d` scripts. This
+# section declares the locations of those files and targets.
 PROFILE_PATH="$BUILD_DIR/.profile.d/python.sh"
 EXPORT_PATH="$BIN_DIR/../export"
 GUNICORN_PROFILE_PATH="$BUILD_DIR/.profile.d/python.gunicorn.sh"
+WEB_CONCURRENCY_PROFILE_PATH="$BUILD_DIR/.profile.d/WEB_CONCURRENCY.sh"
 
 # We'll need to send these statics to other scripts we `source`.
 export BUILD_DIR CACHE_DIR BIN_DIR PROFILE_PATH EXPORT_PATH
 
-# Prepend proper environment variables for Python use.
+# Python Environment Variables
+# Set Python-specific environment variables, for running Python within the buildpack.
+# Notes on each variable included.
+
+# PATH is relatively obvious, we need to be able to execute 'python'.
 export PATH=/app/.heroku/python/bin:/app/.heroku/vendor/bin:$PATH
+# Tell Python to not buffer it's stdin/stdout.
 export PYTHONUNBUFFERED=1
+# Set the locale to a well-known and expected standard.
 export LANG=en_US.UTF-8
+# `~/.heroku/vendor` is an place where the buildpack may stick pre-build binaries for known
+# C dependencies (e.g. libmemcached on cedar-14). This section configures Python (GCC, more specifically)
+# and pip to automatically include these paths when building binaries.
 export C_INCLUDE_PATH=/app/.heroku/vendor/include:/app/.heroku/python/include:$C_INCLUDE_PATH
 export CPLUS_INCLUDE_PATH=/app/.heroku/vendor/include:/app/.heroku/python/include:$CPLUS_INCLUDE_PATH
 export LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LIBRARY_PATH
 export LD_LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LD_LIBRARY_PATH
 export PKG_CONFIG_PATH=/app/.heroku/vendor/lib/pkg-config:/app/.heroku/python/lib/pkg-config:$PKG_CONFIG_PATH
 
+# The Application Code
+# --------------------
+
 # Switch to the repo's context.
-cd $BUILD_DIR
+cd "$BUILD_DIR"
 
-# Warn for lack of Procfile.
-if [[ ! -f Procfile ]]; then
-  puts-warn 'Warning: Your application is missing a Procfile. This file tells Heroku how to run your application.'
-  puts-warn 'Learn more: https://devcenter.heroku.com/articles/procfile'
-fi
+# The Cache
+# ---------
 
-# Experimental pre_compile hook.
-source $BIN_DIR/steps/hooks/pre_compile
+# The workflow for the Python Buildpack's cache is as follows:
+#
+# - `~/.heroku/{known-paths}` are copied from the cache into the slug.
+# - The build is executed, modifying `~/.heroku/{known-paths}`.
+# - Once the build is complete, `~/.heroku/{known-paths}` is copied back into the cache.
 
-# Sticky runtimes.
-if [ -f $CACHE_DIR/.heroku/python-version ]; then
-  DEFAULT_PYTHON_VERSION=$(cat $CACHE_DIR/.heroku/python-version)
-fi
-
-# Stack fallback for non-declared caches.
-if [ -f $CACHE_DIR/.heroku/python-stack ]; then
-  CACHED_PYTHON_STACK=$(cat $CACHE_DIR/.heroku/python-stack)
-else
-  CACHED_PYTHON_STACK=$STACK
-fi
-
-# Pipenv Python version support.
-source $BIN_DIR/steps/pipenv-python-version
-
-# If no runtime given, assume default version.
-if [ ! -f runtime.txt ]; then
-  echo $DEFAULT_PYTHON_VERSION > runtime.txt
-fi
-
-# Prepare the cache.
-mkdir -p $CACHE_DIR
+# Create the cache directory, if it doesn't exist.
+mkdir -p "$CACHE_DIR/.heroku"
 
 # Restore old artifacts from the cache.
 mkdir -p .heroku
 
-cp -R $CACHE_DIR/.heroku/python .heroku/ &> /dev/null || true
-cp -R $CACHE_DIR/.heroku/python-stack .heroku/ &> /dev/null || true
-cp -R $CACHE_DIR/.heroku/python-version .heroku/ &> /dev/null || true
-cp -R $CACHE_DIR/.heroku/vendor .heroku/ &> /dev/null || true
-if [[ -d $CACHE_DIR/.heroku/src ]]; then
-  cp -R $CACHE_DIR/.heroku/src .heroku/ &> /dev/null || true
+# The Python installation.
+cp -R "$CACHE_DIR/.heroku/python" .heroku/ &> /dev/null || true
+# A plain text file which contains the current stack being used (used for cache busting).
+cp -R "$CACHE_DIR/.heroku/python-stack" .heroku/ &> /dev/null || true
+# A plain text file which contains the current python version being used (used for cache busting).
+cp -R "$CACHE_DIR/.heroku/python-version" .heroku/ &> /dev/null || true
+# A plain text file which contains the current sqlite3 version being used (used for cache busting).
+cp -R "$CACHE_DIR/.heroku/python-sqlite3-version" .heroku/ &> /dev/null || true
+# Any pre-compiled binaries, provided by the buildpack.
+cp -R "$CACHE_DIR/.heroku/vendor" .heroku/ &> /dev/null || true
+# "editable" installations of code repositories, via pip or pipenv.
+if [[ -d "$CACHE_DIR/.heroku/src" ]]; then
+  cp -R "$CACHE_DIR/.heroku/src" .heroku/ &> /dev/null || true
 fi
 
+# The pre_compile hook. Customers rely on this. Don't remove it.
+# This part of the code is used to allow users to customize their build experience
+# without forking the buildpack by providing a `bin/pre_compile` script, which gets
+# run inline with the buildpack automatically.
 
-mkdir -p $(dirname $PROFILE_PATH)
+# shellcheck source=bin/steps/hooks/pre_compile
+source "$BIN_DIR/steps/hooks/pre_compile"
+
+# Sticky runtimes. If there was a previous build, and it used a given version of Python,
+# continue to use that version of Python in perpituity (warnings will be raised if
+# they are out–of–date).
+if [ -f "$CACHE_DIR/.heroku/python-version" ]; then
+  DEFAULT_PYTHON_VERSION=$(cat "$CACHE_DIR/.heroku/python-version")
+fi
+
+# We didn't always record the stack version. This code is in place because of that.
+if [ -f "$CACHE_DIR/.heroku/python-stack" ]; then
+  CACHED_PYTHON_STACK=$(cat "$CACHE_DIR/.heroku/python-stack")
+else
+  CACHED_PYTHON_STACK=$STACK
+fi
+
+export CACHED_PYTHON_STACK
+
+# Pipenv Python version support.
+# Detect the version of Python requested from a Pipfile (e.g. python_version or python_full_version).
+# Convert it to a runtime.txt file.
+
+# shellcheck source=bin/steps/pipenv-python-version
+source "$BIN_DIR/steps/pipenv-python-version"
+
+# If no runtime was provided by the user, assume the default Python runtime version.
+if [ ! -f runtime.txt ]; then
+  echo "$DEFAULT_PYTHON_VERSION" > runtime.txt
+fi
+
+# Create the directory for .profile.d, if it doesn't exist.
+mkdir -p "$(dirname "$PROFILE_PATH")"
+# Create the directory for editable source code installation, if it doesn't exist.
 mkdir -p /app/.heroku/src
 
+# On Heroku CI, builds happen in `/app`. Otherwise, on the Heroku platform,
+# they occur in a temp directory. Beacuse Python is not portable, we must create
+# symlinks to emulate that we are operating in `/app` during the build process.
+# This is (hopefully obviously) because apps end up running from `/app` in production.
 if [[ $BUILD_DIR != '/app' ]]; then
     # python expects to reside in /app, so set up symlinks
     # we will not remove these later so subsequent buildpacks can still invoke it
-    ln -nsf $BUILD_DIR/.heroku/python /app/.heroku/python
-    ln -nsf $BUILD_DIR/.heroku/vendor /app/.heroku/vendor
+    ln -nsf "$BUILD_DIR/.heroku/python" /app/.heroku/python
+    ln -nsf "$BUILD_DIR/.heroku/vendor" /app/.heroku/vendor
     # Note: .heroku/src is copied in later.
 fi
 
-# Install Python.
-source $BIN_DIR/steps/python
+# Download / Install Python, from pre-build binaries available on Amazon S3.
+# This step also bootstraps pip / setuptools.
+(( start=$(nowms) ))
+# shellcheck source=bin/steps/python
+source "$BIN_DIR/steps/python"
+mtime "python.install.time" "${start}"
 
-# Sanity check for setuptools/distribute.
-source $BIN_DIR/steps/setuptools
-
-# Pipenv support.
-source $BIN_DIR/steps/pipenv
+# Install Pipenv dependencies, if a Pipfile was provided.
+# shellcheck source=bin/steps/pipenv
+source "$BIN_DIR/steps/pipenv"
 
 # If no requirements.txt file given, assume `setup.py develop` is intended.
+# This allows for people to ship a setup.py application to Heroku
+
 if [ ! -f requirements.txt ] && [ ! -f Pipfile ]; then
   echo "-e ." > requirements.txt
 fi
 
 # Fix egg-links.
-source $BIN_DIR/steps/eggpath-fix
+# Because we're installing things into a different path than we're running them (temp dir vs app dir),
+# We must re-write all of Python's eggpath links to target the proper directory.
+# shellcheck source=bin/steps/eggpath-fix
+source "$BIN_DIR/steps/eggpath-fix"
 
 # Mercurial support.
-source $BIN_DIR/steps/mercurial
+# If a customer appears to be using mercurial for dependency resolution, we install it first.
+# Note: this only applies to pip, not pipenv. This can likely be removed, over time. Measure it first.
+# shellcheck source=bin/steps/mercurial
+source "$BIN_DIR/steps/mercurial"
 
 # Pylibmc support.
-source $BIN_DIR/steps/pylibmc
+# On cedar-14, libmemcached was not available. The buildpack provides its own version, instead.
+# shellcheck source=bin/steps/pylibmc
+source "$BIN_DIR/steps/pylibmc"
 
-# Libffi support.
-source $BIN_DIR/steps/cryptography
-
-# Support for Geo libraries.
-sub-env $BIN_DIR/steps/geo-libs
+# Support for Geo libraries. This is deprecated functionality, only functional on cedar-14.
+# It is undocumented.
+# shellcheck source=bin/steps/geo-libs
+sub_env "$BIN_DIR/steps/geo-libs"
 
 # GDAL support.
-source $BIN_DIR/steps/gdal
+# This is part of the Geo support.
+# shellcheck source=bin/steps/gdal
+source "$BIN_DIR/steps/gdal"
 
-# Install dependencies with Pip (where the magic happens).
-source $BIN_DIR/steps/pip-install
+# SQLite3 support.
+# This sets up and installs sqlite3 dev headers and the sqlite3 binary but not the
+# libsqlite3-0 library since that exists on the stack image.
+# Note: This only applies to Python 2.7.15+ and Python 3.6.6+
+(( start=$(nowms) ))
+# shellcheck source=bin/steps/sqlite3
+source "$BIN_DIR/steps/sqlite3"
+buildpack_sqlite3_install
+mtime "sqlite3.install.time" "${start}"
 
-# Uninstall removed dependencies with Pip.
-source $BIN_DIR/steps/pip-uninstall
+# pip install
+# -----------
+
+# Install dependencies with pip (where the magic happens).
+(( start=$(nowms) ))
+# shellcheck source=bin/steps/pip-install
+source "$BIN_DIR/steps/pip-install"
+mtime "pip.install.time" "${start}"
 
 # Support for NLTK corpora.
-sub-env $BIN_DIR/steps/nltk
+# Note: this may only work on Python 2.7. I don't think many customers use this functionality,
+# and it should probably be undocumented.
+# (there's an import error on 3.6 that should hopefully be fixed upstream at some point)
+(( start=$(nowms) ))
+sub_env "$BIN_DIR/steps/nltk"
+mtime "nltk.download.time" "${start}"
+
+# Support for editable installations. Here, we are copying pip–created src directory,
+# and copying it into the proper place (the logical place to do this was early, but it must be done here).
+# In CI, $BUILD_DIR is /app.
+if [[ ! "$BUILD_DIR" == "/app" ]]; then
+  rm -fr "$BUILD_DIR/.heroku/src"
+  deep-cp /app/.heroku/src "$BUILD_DIR/.heroku/src"
+fi
 
-# Support for pip install -e.
-rm -fr $BUILD_DIR/.heroku/src
-deep-cp /app/.heroku/src $BUILD_DIR/.heroku/src
 
 # Django collectstatic support.
-sub-env $BIN_DIR/steps/collectstatic
+# The buildpack automatically runs collectstatic for Django applications.
+# This is the cause for the majority of build failures on the Python platform.
+# These failures are intentional — if collectstatic (which can be tricky, at times) fails,
+# your build fails.
+(( start=$(nowms) ))
+sub_env "$BIN_DIR/steps/collectstatic"
+mtime "collectstatic.time" "${start}"
 
-# Create .profile script for application runtime environment variables.
-set-env PATH '$HOME/.heroku/python/bin:$PATH'
-set-env PYTHONUNBUFFERED true
-set-env PYTHONHOME /app/.heroku/python
-set-env LIBRARY_PATH '/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LIBRARY_PATH'
-set-env LD_LIBRARY_PATH '/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LD_LIBRARY_PATH'
-set-default-env LANG en_US.UTF-8
-set-default-env PYTHONHASHSEED random
-set-default-env PYTHONPATH /app/
+
+# Progamatically create .profile.d script for application runtime environment variables.
+
+# Set the PATH to include Python / pip / pipenv / etc.
+set_env PATH "\$HOME/.heroku/python/bin:\$PATH"
+# Tell Python to run in unbuffered mode.
+set_env PYTHONUNBUFFERED true
+# Tell Python where it lives.
+set_env PYTHONHOME "\$HOME/.heroku/python"
+# Set variables for C libraries.
+set_env LIBRARY_PATH "\$HOME/.heroku/vendor/lib:\$HOME/.heroku/python/lib:\$LIBRARY_PATH"
+set_env LD_LIBRARY_PATH "\$HOME/.heroku/vendor/lib:\$HOME/.heroku/python/lib:\$LD_LIBRARY_PATH"
+# Locale.
+set_default_env LANG en_US.UTF-8
+# The Python hash seed is set to random.
+set_default_env PYTHONHASHSEED random
+# Tell Python to look for Python modules in the /app dir. Don't change this.
+set_default_env PYTHONPATH "\$HOME"
+
+# Python expects to be in /app, if at runtime, it is not, set
+# up symlinks… this can occur when the subdir buildpack is used.
+cat <<EOT >> "$PROFILE_PATH"
+if [[ \$HOME != "/app" ]]; then
+    mkdir -p /app/.heroku
+    ln -nsf "\$HOME/.heroku/python" /app/.heroku/python
+    ln -nsf "\$HOME/.heroku/vendor" /app/.heroku/vendor
+fi
+EOT
 
 # Install sane-default script for $WEB_CONCURRENCY and $FORWARDED_ALLOW_IPS.
-cp $ROOT_DIR/vendor/python.gunicorn.sh $GUNICORN_PROFILE_PATH
+cp "$ROOT_DIR/vendor/WEB_CONCURRENCY.sh" "$WEB_CONCURRENCY_PROFILE_PATH"
+cp "$ROOT_DIR/vendor/python.gunicorn.sh" "$GUNICORN_PROFILE_PATH"
 
-# Experimental post_compile hook.
-source $BIN_DIR/steps/hooks/post_compile
+# Experimental post_compile hook. Don't remove this.
+# shellcheck source=bin/steps/hooks/post_compile
+source "$BIN_DIR/steps/hooks/post_compile"
 
 # Fix egg-links, again.
-source $BIN_DIR/steps/eggpath-fix2
+# shellcheck source=bin/steps/eggpath-fix2
+source "$BIN_DIR/steps/eggpath-fix2"
 
-# Store new artifacts in cache.
+# Store new artifacts in the cache.
+rm -rf "$CACHE_DIR/.heroku/python"
+rm -rf "$CACHE_DIR/.heroku/python-version"
+rm -rf "$CACHE_DIR/.heroku/python-stack"
+rm -rf "$CACHE_DIR/.heroku/vendor"
+rm -rf "$CACHE_DIR/.heroku/src"
 
-rm -rf $CACHE_DIR/.heroku/python
-rm -rf $CACHE_DIR/.heroku/python-version
-rm -rf $CACHE_DIR/.heroku/python-stack
-rm -rf $CACHE_DIR/.heroku/vendor
-rm -rf $CACHE_DIR/.heroku/src
-
-mkdir -p $CACHE_DIR/.heroku
-cp -R .heroku/python $CACHE_DIR/.heroku/
-cp -R .heroku/python-version $CACHE_DIR/.heroku/
-cp -R .heroku/python-stack $CACHE_DIR/.heroku/ &> /dev/null || true
-cp -R .heroku/vendor $CACHE_DIR/.heroku/ &> /dev/null || true
+mkdir -p "$CACHE_DIR/.heroku"
+cp -R .heroku/python "$CACHE_DIR/.heroku/"
+cp -R .heroku/python-version "$CACHE_DIR/.heroku/"
+cp -R .heroku/python-stack "$CACHE_DIR/.heroku/" &> /dev/null || true
+cp -R .heroku/vendor "$CACHE_DIR/.heroku/" &> /dev/null || true
 if [[ -d .heroku/src ]]; then
-  cp -R .heroku/src $CACHE_DIR/.heroku/ &> /dev/null || true
+  cp -R .heroku/src "$CACHE_DIR/.heroku/" &> /dev/null || true
 fi
+
+# Measure the size of the Python installation.
+# shellcheck disable=SC2119
+mmeasure 'python.size' "$(measure-size)"

bin/default_pythons

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+DEFAULT_PYTHON_VERSION="python-3.6.11"
+LATEST_38="python-3.8.4"
+LATEST_37="python-3.7.8"
+LATEST_36="python-3.6.11"
+LATEST_35="python-3.5.9"
+LATEST_34="python-3.4.10"
+LATEST_27="python-2.7.18"
+PYPY_36="pypy3.6-7.3.1"
+PYPY_27="pypy2.7-7.3.1"
+
+export DEFAULT_PYTHON_VERSION \
+    LATEST_38 \
+    LATEST_37 \
+    LATEST_36 \
+    LATEST_35 \
+    LATEST_34 \
+    LATEST_27 \
+    PYPY_36 \
+    PYPY_27

bin/detect

@@ -15,7 +15,7 @@
 BUILD_DIR=$1
 
 # Exit early if app is clearly not Python.
-if [ ! -f $BUILD_DIR/requirements.txt ] && [ ! -f $BUILD_DIR/setup.py ] && [ ! -f $BUILD_DIR/Pipfile ]; then
+if [ ! -f "$BUILD_DIR/requirements.txt" ] && [ ! -f "$BUILD_DIR/setup.py" ] && [ ! -f "$BUILD_DIR/Pipfile" ]; then
   exit 1
 fi
 

bin/release

@@ -1,10 +1,9 @@
 #!/usr/bin/env bash
 # bin/release <build-dir>
 
-BIN_DIR=$(cd $(dirname $0); pwd) # absolute path
 BUILD_DIR=$1
 
-MANAGE_FILE=$(cd $BUILD_DIR && find . -maxdepth 3 -type f -name 'manage.py' | head -1)
+MANAGE_FILE=$(cd "$BUILD_DIR" && find . -maxdepth 3 -type f -name 'manage.py' | head -1)
 MANAGE_FILE=${MANAGE_FILE:2}
 
 cat <<EOF

bin/steps/README.MD

@@ -0,0 +1,28 @@
+# Python Buildpack Install Steps
+
+TODO: Add context on Python install steps, such as why symlinking vs copying
+
+## Installing the Pip tool
+
+The Python Buildpack uses a tool called `get-pip` to install the pip tool. This
+is done in the `python` script.
+
+This is in part because Python historically did not come with pip by default.
+
+## Installing Python packages using Pip
+
+### Convention: Use `python` process to invoke Pip
+
+We don't use this convention (yet) but this is an upcoming change being considered.
+
+This is a bigger concern on Windows than it is in Linux environments, but an
+emerging convention in the Python community is to invoke pip using:
+
+```
+python3 -m pip [options]
+```
+
+Invoking pip this way ensures correct location - python knows where these
+packages are stored because it put them there (defaults to Python's pathing info).
+
+All normal command line options are available using this method.

bin/steps/collectstatic

@@ -10,7 +10,8 @@
 #   - $DISABLE_COLLECTSTATIC: disables this functionality.
 #   - $DEBUG_COLLECTSTATIC: upon failure, print out environment variables.
 
-source $BIN_DIR/utils
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
 # Location of 'manage.py', if it exists.
 MANAGE_FILE=$(find . -maxdepth 3 -type f -name 'manage.py' -printf '%d\t%P\n' | sort -nk1 | cut -f2 | head -1)
@@ -20,22 +21,44 @@ MANAGE_FILE=${MANAGE_FILE:-fakepath}
 [ -f .heroku/collectstatic_disabled ] && DISABLE_COLLECTSTATIC=1
 
 # Ensure that Django is explicitly specified in requirements.txt
-pip-grep -s requirements.txt django Django && DJANGO_INSTALLED=1
+sp-grep -s django && DJANGO_INSTALLED=1
 
 
 if [ ! "$DISABLE_COLLECTSTATIC" ] && [ -f "$MANAGE_FILE" ] && [ "$DJANGO_INSTALLED" ]; then
     set +e
 
-    puts-cmd "python $MANAGE_FILE collectstatic --noinput"
+    puts-step "$ python $MANAGE_FILE collectstatic --noinput"
 
     # Run collectstatic, cleanup some of the noisy output.
-    python $MANAGE_FILE collectstatic --noinput --traceback 2>&1 | sed '/^Post-processed/d;/^Copying/d;/^$/d' | indent
+    PYTHONPATH=${PYTHONPATH:-.}
+    export PYTHONPATH
+
+    # Create a temporary file for collecting the collectstaic logs.
+    COLLECTSTATIC_LOG=$(mktemp)
+
+    python "$MANAGE_FILE" collectstatic --noinput --traceback 2>&1 | tee "$COLLECTSTATIC_LOG" | sed '/^Post-processed/d;/^Copying/d;/^$/d' | indent
     COLLECTSTATIC_STATUS="${PIPESTATUS[0]}"
 
     set -e
 
     # Display a warning if collectstatic failed.
-    [ $COLLECTSTATIC_STATUS -ne 0 ] && {
+    [ "$COLLECTSTATIC_STATUS" -ne 0 ] && {
+
+        if grep -q 'SyntaxError' "$COLLECTSTATIC_LOG"; then
+            mcount "failure.collectstatic.syntax-error"
+
+        elif grep -q 'ImproperlyConfigured' "$COLLECTSTATIC_LOG"; then
+            mcount "failure.collectstatic.improper-configuration"
+
+        elif grep -q 'The CSS file' "$COLLECTSTATIC_LOG"; then
+            mcount "failure.collectstatic.fancy-references"
+
+        elif grep -q 'OSError' "$COLLECTSTATIC_LOG"; then
+            mcount "failure.collectstatic.missing-file"
+
+        else
+            mcount "failure.collectstatic.other"
+        fi
 
         echo
         echo " !     Error while running '$ python $MANAGE_FILE collectstatic --noinput'."

bin/steps/cryptography

@@ -1,31 +0,0 @@
-#!/usr/bin/env bash
-
-# This script serves as the Cryptography build step of the
-# [**Python Buildpack**](https://github.com/heroku/heroku-buildpack-python)
-# compiler.
-#
-# A [buildpack](https://devcenter.heroku.com/articles/buildpacks) is an
-# adapter between a Python application and Heroku's runtime.
-#
-# This script is invoked by [`bin/compile`](/).
-
-# The location of the pre-compiled libffi binary.
-VENDORED_LIBFFI="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/libffi.tar.gz"
-
-PKG_CONFIG_PATH="/app/.heroku/vendor/lib/pkgconfig:$PKG_CONFIG_PATH"
-
-# Syntax sugar.
-source $BIN_DIR/utils
-
-# If a package using cffi exists within requirements, use vendored libffi.
-if (pip-grep -s requirements.txt argon2-cffi bcrypt cffi cryptography django[argon2] Django[argon2] django[bcrypt] Django[bcrypt] PyNaCl pyOpenSSL PyOpenSSL requests[security] misaka &> /dev/null) then
-
-  if [ ! -d ".heroku/vendor/lib/libffi-3.1" ]; then
-    echo "-----> Noticed cffi. Bootstrapping libffi."
-    mkdir -p .heroku/vendor
-    # Download and extract libffi into target vendor directory.
-    curl $VENDORED_LIBFFI -s | tar zxv -C .heroku/vendor &> /dev/null
-  fi
-
-  export LIBFFI=$(pwd)/vendor
-fi

bin/steps/eggpath-fix

@@ -1,3 +1,5 @@
+#!/usr/bin/env bash
+
 set +e
 # delete any existing egg links, to uninstall exisisting installations.
 find .heroku/python/lib/python*/site-packages/ -name "*.egg-link" -delete 2> /dev/null

bin/steps/eggpath-fix2

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 set +e
 # rewrite build dir in egg links to /app so things are found at runtime
 find .heroku/python/lib/python*/site-packages/ -name "*.pth" -print0 2> /dev/null | xargs -r -0 -n 1 sed -i -e "s#$(pwd)#/app#" &> /dev/null

bin/steps/gdal

@@ -10,23 +10,29 @@
 # This script is invoked by [`bin/compile`](/).
 
 # The location of the pre-compiled cryptography binary.
-VENDORED_GDAL="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/gdal.tar.gz"
+VENDORED_GDAL="${VENDOR_URL}/libraries/vendor/gdal.tar.gz"
 
 PKG_CONFIG_PATH="/app/.heroku/vendor/lib/pkgconfig:$PKG_CONFIG_PATH"
 
 # Syntax sugar.
-source $BIN_DIR/utils
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
 # If GDAL exists within requirements, use vendored gdal.
 if (pip-grep -s requirements.txt GDAL gdal pygdal &> /dev/null) then
 
   if [ ! -f ".heroku/vendor/bin/gdalserver" ]; then
+
+    puts-warn "The vendored GDAL package in the Heroku Python Buildpack now deprecated."
+    puts-warn "To enable GDAL use an alternative buildpack is available here - https://github.com/heroku/heroku-geo-buildpack"
+
     echo "-----> Noticed GDAL. Bootstrapping gdal."
     mkdir -p .heroku/vendor
     # Download and extract cryptography into target vendor directory.
-    curl $VENDORED_GDAL -s | tar zxv -C .heroku/vendor &> /dev/null
+    curl "$VENDORED_GDAL" -s | tar zxv -C .heroku/vendor &> /dev/null
+    mcount "steps.vendor.gdal"
   fi
 
-  export GDAL=$(pwd)/vendor
+  GDAL=$(pwd)/vendor
+  export GDAL
 fi
-

bin/steps/geo-libs

@@ -10,27 +10,46 @@
 # This script is invoked by [`bin/compile`](/).
 
 # The location of the pre-compiled cryptography binary.
-VENDORED_GDAL="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/gdal.tar.gz"
-VENDORED_GEOS="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/geos.tar.gz"
-VENDORED_PROJ="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/proj.tar.gz"
+VENDORED_GDAL="${VENDOR_URL}/libraries/vendor/gdal.tar.gz"
+VENDORED_GEOS="${VENDOR_URL}/libraries/vendor/geos.tar.gz"
+VENDORED_PROJ="${VENDOR_URL}/libraries/vendor/proj.tar.gz"
 
 PKG_CONFIG_PATH="/app/.heroku/vendor/lib/pkgconfig:$PKG_CONFIG_PATH"
 
 # Syntax sugar.
-source $BIN_DIR/utils
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
 # If GDAL exists within requirements, use vendored gdal.
 if [[ "$BUILD_WITH_GEO_LIBRARIES" ]]; then
+  mcount "buildvar.BUILD_WITH_GEO_LIBRARIES"
+
+  puts-warn "The GDAL, GEOS and PROJ binaries and BUILD_WITH_GEO_LIBRARIES functonality are now deprecated."
+  puts-warn "An alternative buildpack to enable GDAL, GEOS and PROJ use is available here - https://github.com/heroku/heroku-geo-buildpack"
 
   if [ ! -f ".heroku/vendor/bin/proj" ]; then
     echo "-----> Bootstrapping gdal, geos, proj."
     mkdir -p .heroku/vendor
     # Download and extract cryptography into target vendor directory.
-    curl $VENDORED_GDAL -s | tar zxv -C .heroku/vendor &> /dev/null
-    curl $VENDORED_GEOS -s | tar zxv -C .heroku/vendor &> /dev/null
-    curl $VENDORED_PROJ -s | tar zxv -C .heroku/vendor &> /dev/null
+    curl "$VENDORED_GDAL" -s | tar zxv -C .heroku/vendor &> /dev/null
+    curl "$VENDORED_GEOS" -s | tar zxv -C .heroku/vendor &> /dev/null
+    curl "$VENDORED_PROJ" -s | tar zxv -C .heroku/vendor &> /dev/null
+
+    mcount "steps.vendor.geo_libs"
+    # Copy libjasper from build image to slug.
+    if [[ "$STACK" == "heroku-16" ]]; then
+      cp /usr/lib/x86_64-linux-gnu/libjasper.so* ".heroku/vendor/lib/."
+      mcount "steps.vendor.libjasper"
+    fi
+
   fi
 
-  export GDAL=$(pwd)/vendor
+  GDAL=$(pwd)/vendor
+  export GDAL
+  # set path for post_compile hooks
+  export GDAL_LIBRARY_PATH="$BUILD_DIR/.heroku/vendor/lib/libgdal.so"
+  export GEOS_LIBRARY_PATH="$BUILD_DIR/.heroku/vendor/lib/libgeos_c.so"
+  # set path for runtime environmeht
+  set_env GDAL_LIBRARY_PATH "/app/.heroku/vendor/lib/libgdal.so"
+  set_env GEOS_LIBRARY_PATH "/app/.heroku/vendor/lib/libgeos_c.so"
 fi
-

bin/steps/hooks/post_compile

@@ -3,5 +3,5 @@
 if [ -f bin/post_compile ]; then
     echo "-----> Running post-compile hook"
     chmod +x bin/post_compile
-    sub-env bin/post_compile
+    sub_env bin/post_compile
 fi

bin/steps/hooks/pre_compile

@@ -3,5 +3,5 @@
 if [ -f bin/pre_compile ]; then
     echo "-----> Running pre-compile hook"
     chmod +x bin/pre_compile
-    sub-env bin/pre_compile
+    sub_env bin/pre_compile
 fi

bin/steps/mercurial

@@ -1,4 +1,9 @@
+#!/usr/bin/env bash
+
 # Install Mercurial if it appears to be required.
-if (grep -Fiq "hg+" requirements.txt) then
-    /app/.heroku/python/bin/pip install  mercurial | cleanup | indent
+if [[ -f "requirements.txt" ]]; then
+	if (grep -Fiq "hg+" requirements.txt) then
+		/app/.heroku/python/bin/pip install  mercurial | cleanup | indent
+		mcount "steps.mercurial"
+	fi
 fi

bin/steps/nltk

@@ -10,21 +10,27 @@
 # This script is invoked by [`bin/compile`](/).
 
 # Syntax sugar.
-source $BIN_DIR/utils
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
 # Check that nltk was installed by pip, otherwise obviously not needed
-python -m nltk.downloader -h >/dev/null 2>&1
-if [ $? -eq 0 ]; then
-    puts-step "Downloading NLTK corpora..."
+if sp-grep -s nltk; then
+    puts-step "Downloading NLTK corpora…"
+
     nltk_packages_definition="$BUILD_DIR/nltk.txt"
+
     if [ -f "$nltk_packages_definition" ]; then
-        nltk_packages=$(tr "\n" " " < "$nltk_packages_definition")
-        puts-step "Downloading NLTK packages: $nltk_packages"
-        python -m nltk.downloader -d $BUILD_DIR/.heroku/python/nltk_data $nltk_packages  | indent
-        set-env NLTK_DATA "/app/.heroku/python/nltk_data"
+
+        readarray -t nltk_packages < "$nltk_packages_definition"
+        puts-step "Downloading NLTK packages: ${nltk_packages[*]}"
+
+        python -m nltk.downloader -d "$BUILD_DIR/.heroku/python/nltk_data" "${nltk_packages[@]}" | indent
+        set_env NLTK_DATA "/app/.heroku/python/nltk_data"
+
+        mcount "buildvar.NLTK_PACKAGES_DEFINITION"
+        mcount "steps.nltk"
     else
         puts-warn "'nltk.txt' not found, not downloading any corpora"
         puts-warn "Learn more: https://devcenter.heroku.com/articles/python-nltk"
     fi
 fi
-

bin/steps/pip-install

@@ -1,20 +1,72 @@
-# Install dependencies with Pip.
-puts-step "Installing requirements with pip"
+#!/usr/bin/env bash
 
-set +e
-/app/.heroku/python/bin/pip install -r $BUILD_DIR/requirements.txt --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee $WARNINGS_LOG | cleanup | indent
-PIP_STATUS="${PIPESTATUS[0]}"
-set -e
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
-show-warnings
+if [ ! "$SKIP_PIP_INSTALL" ]; then
 
-if [[ ! $PIP_STATUS -eq 0 ]]; then
-    exit 1
+    # Install dependencies with Pip.
+    puts-step "Installing requirements with pip"
+
+    # Set Pip env vars
+    # This reads certain environment variables set on the Heroku app config
+    # and makes them accessible to the pip install process.
+    #
+    # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
+    if [[ -r "$ENV_DIR/PIP_EXTRA_INDEX_URL" ]]; then
+        PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
+        export PIP_EXTRA_INDEX_URL
+        mcount "buildvar.PIP_EXTRA_INDEX_URL"
+    fi
+
+    set +e
+
+    # Set SLUGIFY_USES_TEXT_UNIDECODE, required for Airflow versions >=1.10
+    if [[ -r "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE" ]]; then
+        SLUGIFY_USES_TEXT_UNIDECODE="$(cat "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE")"
+        export SLUGIFY_USES_TEXT_UNIDECODE
+        mcount "buildvar.SLUGIFY_USES_TEXT_UNIDECODE"
+    fi
+
+    set +e
+
+    # Measure that we're using pip.
+    mcount "tool.pip"
+
+    # Count expected build failures.
+    if grep -q '==0.0.0' requirements.txt; then
+        mcount "failure.none-version"
+    fi
+
+    if grep -qi '^django==1.*' requirements.txt; then
+        puts-warn "Your Django version is nearing the end of its community support."
+        puts-warn "Upgrade to continue to receive security updates and for the best experience with Django."
+        puts-warn "For more information, check out https://www.djangoproject.com/download/#supported-versions"
+    fi
+
+    if [ ! -f "$BUILD_DIR/.heroku/python/bin/pip" ]; then
+        exit 1
+    fi
+
+    /app/.heroku/python/bin/pip install -r "$BUILD_DIR/requirements.txt" --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
+    PIP_STATUS="${PIPESTATUS[0]}"
+    set -e
+
+    show-warnings
+
+    if [[ ! $PIP_STATUS -eq 0 ]]; then
+        mcount "failure.pip-install"
+        exit 1
+    fi
+
+    cp requirements.txt .heroku/python/requirements-declared.txt
+    /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
+
+    # Install test dependencies, for CI.
+    if [ "$INSTALL_TEST" ]; then
+        if [[ -f "$1/requirements-test.txt" ]]; then
+            puts-step "Installing test dependencies…"
+            /app/.heroku/python/bin/pip install -r "$1/requirements-test.txt" --exists-action=w --src=./.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | cleanup | indent
+        fi
+    fi
 fi
-
-
-# Smart Requirements handling
-cp requirements.txt .heroku/python/requirements-declared.txt
-/app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
-
-echo

bin/steps/pip-uninstall

@@ -1,18 +1,28 @@
+#!/usr/bin/env bash
+
 set +e
 # Install dependencies with Pip.
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
-if [[ -f .heroku/python/requirements-declared.txt ]]; then
+if [ ! "$SKIP_PIP_INSTALL" ]; then
 
-  cp .heroku/python/requirements-declared.txt requirements-declared.txt
+  if [[ -f .heroku/python/requirements-declared.txt ]]; then
 
-  pip-diff --stale requirements-declared.txt requirements.txt --exclude setuptools pip wheel > .heroku/python/requirements-stale.txt
+    cp .heroku/python/requirements-declared.txt requirements-declared.txt
 
-  rm -fr requirements-declared.txt
 
-  if [[ -s .heroku/python/requirements-stale.txt ]]; then
-    puts-step "Uninstalling stale dependencies"
-    /app/.heroku/python/bin/pip uninstall -r .heroku/python/requirements-stale.txt -y --exists-action=w | cleanup | indent
+    if ! pip-diff --stale requirements-declared.txt requirements.txt --exclude setuptools pip wheel > .heroku/python/requirements-stale.txt; then
+      mcount "failure.bad-requirements"
+    fi
+
+    rm -fr requirements-declared.txt
+
+    if [[ -s .heroku/python/requirements-stale.txt ]]; then
+      puts-step "Uninstalling stale dependencies"
+      /app/.heroku/python/bin/pip uninstall -r .heroku/python/requirements-stale.txt -y --exists-action=w --disable-pip-version-check | cleanup | indent
+    fi
   fi
-fi
 
+fi
 set -e

bin/steps/pipenv

@@ -1,10 +1,86 @@
-# Pipenv support (Generate requriements.txt with pipenv).
-if [[ -f Pipfile ]]; then
-    if [[ ! -f requirements.txt ]]; then
-        puts-step "Generating 'requirements.txt' with pipenv"
+#!/usr/bin/env bash
 
-        /app/.heroku/python/bin/pip install pipenv --upgrade &> /dev/null
+# export CLINT_FORCE_COLOR=1
+# export PIPENV_FORCE_COLOR=1
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
+set -e
 
-        /app/.heroku/python/bin/pipenv lock --requirements --no-hashes > $BUILD_DIR/requirements.txt 2> /dev/null
+if [[ -f Pipfile.lock ]]; then
+    if [[ -f .heroku/python/Pipfile.lock.sha256 ]]; then
+        if [[ $(openssl dgst -sha256 Pipfile.lock) == $(cat .heroku/python/Pipfile.lock.sha256) ]]; then
+            # Measure that we're using Pipenv.
+            mcount "tool.pipenv"
+
+            # Don't skip installation of there are git deps.
+            if ! grep -q 'git' Pipfile.lock; then
+                echo "Skipping installation, as Pipfile.lock hasn't changed since last deploy." | indent
+
+                mcount "tool.pipenv"
+                export SKIP_PIPENV_INSTALL=1
+                export SKIP_PIP_INSTALL=1
+            fi
+        fi
     fi
-fi
+fi
+
+
+if [ ! "$SKIP_PIPENV_INSTALL" ]; then
+    # Pipenv support (Generate requirements.txt with pipenv).
+    if [[ -f Pipfile ]]; then
+        # Measure that we're using Pipenv.
+        mcount "tool.pipenv"
+
+        # Skip pip install, later.
+        export SKIP_PIP_INSTALL=1
+
+        # Set Pip env vars
+        # This reads certain environment variables set on the Heroku app config
+        # and makes them accessible to the pip install process.
+        #
+        # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
+        if [[ -r "$ENV_DIR/PIP_EXTRA_INDEX_URL" ]]; then
+            PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
+            export PIP_EXTRA_INDEX_URL
+            mcount "buildvar.PIP_EXTRA_INDEX_URL"
+        fi
+
+        # Set SLUGIFY_USES_TEXT_UNIDECODE, required for Airflow versions >=1.10
+        if [[ -r "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE" ]]; then
+            SLUGIFY_USES_TEXT_UNIDECODE="$(cat "$ENV_DIR/SLUGIFY_USES_TEXT_UNIDECODE")"
+            export SLUGIFY_USES_TEXT_UNIDECODE
+            mcount "buildvar.SLUGIFY_USES_TEXT_UNIDECODE"
+        fi
+
+        export PIPENV_VERSION="2018.5.18"
+
+        # Install pipenv.
+        # Due to weird old pip behavior and pipenv behavior, pipenv upgrades pip
+        # to latest if only --upgrade is specified. Specify upgrade strategy to
+        # avoid this eager behavior.
+        /app/.heroku/python/bin/pip install pipenv==$PIPENV_VERSION --upgrade --upgrade-strategy only-if-needed &> /dev/null
+
+        # Install the test dependencies, for CI.
+        if [ "$INSTALL_TEST" ]; then
+            puts-step "Installing test dependencies…"
+            /app/.heroku/python/bin/pipenv install --dev --system --deploy 2>&1 | cleanup | indent
+
+        # Install the dependencies.
+        elif [[ ! -f Pipfile.lock ]]; then
+            puts-step "Installing dependencies with Pipenv $PIPENV_VERSION…"
+            /app/.heroku/python/bin/pipenv install --system --skip-lock 2>&1 | indent
+
+        else
+            pipenv-to-pip Pipfile.lock > requirements.txt
+            "$BIN_DIR/steps/pip-uninstall"
+            cp requirements.txt .heroku/python/requirements-declared.txt
+            openssl dgst -sha256 Pipfile.lock > .heroku/python/Pipfile.lock.sha256
+
+            puts-step "Installing dependencies with Pipenv $PIPENV_VERSION…"
+            /app/.heroku/python/bin/pipenv install --system --deploy 2>&1 | indent
+        fi
+    fi
+else
+    export SKIP_PIP_INSTALL=1
+    pipenv-to-pip Pipfile.lock > requirements.txt
+fi

bin/steps/pipenv-python-version

@@ -1,23 +1,38 @@
+#!/usr/bin/env bash
+
 # Detect Python-version with Pipenv.
 
-if [[ -f $BUILD_DIR/Pipfile.lock ]]; then
+if [[ -f $BUILD_DIR/Pipfile ]]; then
 
     if [[ ! -f $BUILD_DIR/runtime.txt ]]; then
         if [[ ! -f $BUILD_DIR/Pipfile.lock ]]; then
-            puts-warn "No 'pipfile.lock' found! We recommend you commit this into your repository."
+            puts-warn "No 'Pipfile.lock' found! We recommend you commit this into your repository."
         fi
         if [[ -f $BUILD_DIR/Pipfile.lock ]]; then
             set +e
-            PYTHON=$(cat $BUILD_DIR/Pipfile.lock | jq '._meta.requires.python_version' -r)
+            PYTHON=$(jq -r '._meta.requires.python_full_version' "$BUILD_DIR/Pipfile.lock")
+            if [[ "$PYTHON" != "null" ]]; then
+                echo "python-$PYTHON" > "$BUILD_DIR/runtime.txt"
+            fi
             set -e
 
-            if [ "$PYTHON" = 2.7 ]; then
-                echo "python-2.7.13" > $BUILD_DIR/runtime.txt
-            fi
-            if [ "$PYTHON" = 3.6 ]; then
-                echo "python-3.6.0" > $BUILD_DIR/runtime.txt
+            if [[ "$PYTHON" == "null" ]]; then
+                PYTHON=$(jq -r '._meta.requires.python_version' "$BUILD_DIR/Pipfile.lock")
+                if [ "$PYTHON" = 2.7 ]; then
+                    echo "$LATEST_27" > "$BUILD_DIR/runtime.txt"
+                fi
+                if [ "$PYTHON" = 3.6 ]; then
+                    echo "$LATEST_36" > "$BUILD_DIR/runtime.txt"
+                fi
+                if [ "$PYTHON" = 3.7 ]; then
+                    echo "$LATEST_37" > "$BUILD_DIR/runtime.txt"
+                fi
+                if [ "$PYTHON" = 3.8 ]; then
+                    echo "$LATEST_38" > "$BUILD_DIR/runtime.txt"
+                fi
             fi
+
+
         fi
     fi
 fi
-

bin/steps/pylibmc

@@ -9,12 +9,17 @@
 #
 # This script is invoked by [`bin/compile`](/).
 
+if [[ "$STACK" != "cedar-14" ]]; then
+    # libmemcached is pre-installed in the stack image so there is no need to vendor it.
+    return 0
+fi
+
 # The location of the pre-compiled libmemcached binary.
-VENDORED_MEMCACHED="https://lang-python.s3.amazonaws.com/$STACK/libraries/vendor/libmemcache.tar.gz"
+VENDORED_MEMCACHED="${VENDOR_URL}/libraries/vendor/libmemcache.tar.gz"
 
 # Syntax sugar.
-source $BIN_DIR/utils
-
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
 # If pylibmc exists within requirements, use vendored libmemcached.
 if (pip-grep -s requirements.txt pylibmc &> /dev/null) then
@@ -23,8 +28,10 @@ if (pip-grep -s requirements.txt pylibmc &> /dev/null) then
     echo "-----> Noticed pylibmc. Bootstrapping libmemcached."
     mkdir -p .heroku/vendor
     # Download and extract libmemcached into target vendor directory.
-    curl $VENDORED_MEMCACHED -s | tar zxv -C .heroku/vendor &> /dev/null
+    curl "$VENDORED_MEMCACHED" -s | tar zxv -C .heroku/vendor &> /dev/null
+    mcount "steps.vendor.pylibmc"
   fi
 
-  export LIBMEMCACHED=$(pwd)/vendor
+  LIBMEMCACHED=$(pwd)/vendor
+  export LIBMEMCACHED
 fi

bin/steps/python

@@ -1,10 +1,93 @@
+#!/usr/bin/env bash
+
 set +e
 runtime-fixer runtime.txt
 PYTHON_VERSION=$(cat runtime.txt)
 
-# Install Python.
+# The location of the pre-compiled python binary.
+VENDORED_PYTHON="${VENDOR_URL}/runtimes/$PYTHON_VERSION.tar.gz"
+
+SECURITY_UPDATE="Python has released a security update! Please consider upgrading to"
+
+ONLY_SUPPORTED_2_VERSION="Only the latest version of Python 2 is supported on the platform. Please consider upgrading to"
+
+PYTHON_2_EOL_UPDATE="Python 2 has reached it's community EOL. Upgrade your Python runtime to maintain a secure application as soon as possible."
+
+# check if runtime exists
+if curl --output /dev/null --silent --head --fail "$VENDORED_PYTHON"; then
+  if [[ "$PYTHON_VERSION" == $PY38* ]]; then
+    # do things to alert the user of security release available
+    if [ "$PYTHON_VERSION" != "$LATEST_38" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_38"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PY37* ]]; then
+    # do things to alert the user of security release available
+    if [ "$PYTHON_VERSION" != "$LATEST_37" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_37"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PY36* ]]; then
+    # security update note
+    if [ "$PYTHON_VERSION" != "$LATEST_36" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_36"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PY35* ]]; then
+    # security update note
+    if [ "$PYTHON_VERSION" != "$LATEST_35" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_35"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PY34* ]]; then
+    # security update note
+    if [ "$PYTHON_VERSION" != "$LATEST_34" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_34"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PY27* ]]; then
+    # security update note
+    if [[ "$(date "+%Y")" -gt "2019" ]]; then
+      puts-warn "$PYTHON_2_EOL_UPDATE"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-2-7-eol-faq"
+    fi
+    if [ "$PYTHON_VERSION" != "$LATEST_27" ]; then
+      puts-warn "$ONLY_SUPPORTED_2_VERSION" "$LATEST_27"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PYPY27* ]]; then
+    # security update note
+    if [ "$PYTHON_VERSION" != "$PYPY_27" ]; then
+      puts-warn "Could not find that Pypy version. Did you mean" "${PYPY_27}?"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+  if [[ "$PYTHON_VERSION" == $PYPY36* ]]; then
+    # security update note
+    if [ "$PYTHON_VERSION" != "$PYPY_36" ]; then
+      puts-warn "Could not find that Pypy version. Did you mean" "${PYPY_36}?"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
+else
+  puts-warn "Requested runtime ($PYTHON_VERSION) is not available for this stack ($STACK)."
+  puts-warn "Aborting.  More info: https://devcenter.heroku.com/articles/python-support"
+  exit 1
+fi
+
+if [[ "$STACK" != "$CACHED_PYTHON_STACK" ]]; then
+    puts-step "Stack has changed from $CACHED_PYTHON_STACK to $STACK, clearing cache"
+    rm -fr .heroku/python-stack .heroku/python-version .heroku/python .heroku/vendor .heroku/python .heroku/python-sqlite3-version
+fi
+
 if [ -f .heroku/python-version ]; then
-  if [ ! $(cat .heroku/python-version) = $PYTHON_VERSION ]; then
+  if [ ! "$(cat .heroku/python-version)" = "$PYTHON_VERSION" ]; then
       puts-step "Found $(cat .heroku/python-version), removing"
       rm -fr .heroku/python
   else
@@ -12,48 +95,69 @@ if [ -f .heroku/python-version ]; then
   fi
 fi
 
-if [ ! $STACK = $CACHED_PYTHON_STACK ]; then
-    rm -fr .heroku/python .heroku/python-stack .heroku/vendor
+# Check if we should reinstall python dependencies
+if [[ ! -f "$CACHE_DIR/.heroku/requirements.txt" ]]; then
+  # IF there's no cached dependencies, update cached version of requirements.txt
+  # This should only run for new apps and first deploys after this update
+  cp -R "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt"
+else
+  # IF there IS a cached directory, check for differences with the new one
+  if ! diff "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt" &> /dev/null; then
+    puts-step "Requirements file has been changed, clearing cached dependencies"
+    # if there are any differences, clear the Python cache
+    # Installing Python over again does not take noticably more time
+    cp -R "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt"
+    rm -rf .heroku/python
     unset SKIP_INSTALL
+  else
+    puts-step "No change in requirements detected, installing from cache"
+  fi
 fi
 
-
 if [ ! "$SKIP_INSTALL" ]; then
     puts-step "Installing $PYTHON_VERSION"
 
     # Prepare destination directory.
     mkdir -p .heroku/python
 
-    curl https://lang-python.s3.amazonaws.com/$STACK/runtimes/$PYTHON_VERSION.tar.gz -s | tar zxv -C .heroku/python &> /dev/null
-    if [[ $? != 0 ]] ; then
+    mcount "version.python.$PYTHON_VERSION"
+
+    if ! curl "${VENDORED_PYTHON}" -s | tar zxv -C .heroku/python &> /dev/null; then
       puts-warn "Requested runtime ($PYTHON_VERSION) is not available for this stack ($STACK)."
       puts-warn "Aborting.  More info: https://devcenter.heroku.com/articles/python-support"
       exit 1
     fi
 
   # Record for future reference.
-  echo $PYTHON_VERSION > .heroku/python-version
-  echo $STACK > .heroku/python-stack
+  echo "$PYTHON_VERSION" > .heroku/python-version
+  echo "$STACK" > .heroku/python-stack
   FRESH_PYTHON=true
 
   hash -r
 fi
 
-# If Pip isn't up to date:
-if [ "$FRESH_PYTHON" ] || [[ ! $(pip --version) == *$PIP_VERSION* ]]; then
-  WORKING_DIR=$(pwd)
+# Heroku uses the get-pip utility maintained by the Python community to vendor Pip.
+# https://github.com/pypa/get-pip
+GETPIP_URL="https://lang-python.s3.amazonaws.com/etc/get-pip.py"
+GETPIP_PY="${TMPDIR:-/tmp}/get-pip.py"
 
-  TMPTARDIR=$(mktemp -d)
-  trap "rm -rf $TMPTARDIR" RETURN
+if ! curl -s "${GETPIP_URL}" -o "$GETPIP_PY" &> /dev/null; then
+    mcount "failure.python.get-pip"
+    echo "Failed to pull down get-pip"
+    exit 1
+fi
+
+# If a new Python has been installed or Pip isn't up to date:
+if [ "$FRESH_PYTHON" ] || [[ ! $(pip --version) == *$PIP_UPDATE* ]]; then
 
   puts-step "Installing pip"
 
   # Remove old installations.
-  rm -fr /app/.heroku/python/lib/python2.7/site-packages/pip-*
-  rm -fr /app/.heroku/python/lib/python2.7/site-packages/setuptools-*
-
-  /app/.heroku/python/bin/python $ROOT_DIR/vendor/get-pip.py &> /dev/null
+  rm -fr /app/.heroku/python/lib/python*/site-packages/pip-*
+  rm -fr /app/.heroku/python/lib/python*/site-packages/setuptools-*
 
+  /app/.heroku/python/bin/python "$GETPIP_PY" pip=="$PIP_UPDATE" &> /dev/null
+  /app/.heroku/python/bin/pip install "$ROOT_DIR/vendor/setuptools-39.0.1-py2.py3-none-any.whl" &> /dev/null
 fi
 
 set -e

bin/steps/setuptools

@@ -1,11 +0,0 @@
-#!/usr/bin/env bash
-
-# Syntax sugar.
-source $BIN_DIR/utils
-
-if (pip-grep -s requirements.txt setuptools distribute &> /dev/null) then
-
-  puts-warn 'The package setuptools/distribute is listed in requirements.txt.'
-  puts-warn 'Please remove to ensure expected behavior. '
-
-fi

bin/steps/sqlite3

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
+
+sqlite3_install() {
+  HEROKU_PYTHON_DIR="$1"
+  HEADERS_ONLY="$3"
+
+  mkdir -p "$HEROKU_PYTHON_DIR"
+
+  APT_CACHE_DIR="$HEROKU_PYTHON_DIR/apt/cache"
+  APT_STATE_DIR="$HEROKU_PYTHON_DIR/apt/state"
+
+  mkdir -p "$APT_CACHE_DIR/archives/partial"
+  mkdir -p "$APT_STATE_DIR/lists/partial"
+
+  APT_OPTIONS="-o debug::nolocking=true"
+  APT_OPTIONS="$APT_OPTIONS -o dir::cache=$APT_CACHE_DIR"
+  APT_OPTIONS="$APT_OPTIONS -o dir::state=$APT_STATE_DIR"
+  APT_OPTIONS="$APT_OPTIONS -o dir::etc::sourcelist=/etc/apt/sources.list"
+
+  apt-get $APT_OPTIONS update > /dev/null 2>&1
+  if [ -z "$HEADERS_ONLY" ]; then
+    apt-get $APT_OPTIONS -y -d --reinstall install libsqlite3-dev sqlite3 > /dev/null 2>&1
+  else
+    apt-get $APT_OPTIONS -y -d --reinstall install libsqlite3-dev
+  fi
+
+  find "$APT_CACHE_DIR/archives/" -name "*.deb" -exec dpkg -x {} "$HEROKU_PYTHON_DIR/sqlite3/" \;
+
+  mkdir -p "$HEROKU_PYTHON_DIR/include"
+  mkdir -p "$HEROKU_PYTHON_DIR/lib"
+
+  # remove old sqlite3 libraries/binaries
+  find "$HEROKU_PYTHON_DIR/include/" -name "sqlite3*.h" -exec rm -f {} \;
+  find "$HEROKU_PYTHON_DIR/lib/" -name "libsqlite3.*" -exec rm -f {} \;
+  rm -f "$HEROKU_PYTHON_DIR/lib/pkgconfig/sqlite3.pc"
+  rm -f "$HEROKU_PYTHON_DIR/bin/sqlite3"
+
+  # copy over sqlite3 headers & bins and setup linking against the stack image library
+  mv "$HEROKU_PYTHON_DIR/sqlite3/usr/include/"* "$HEROKU_PYTHON_DIR/include/"
+  mv "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/x86_64-linux-gnu"/libsqlite3.*a "$HEROKU_PYTHON_DIR/lib/"
+  mkdir -p "$HEROKU_PYTHON_DIR/lib/pkgconfig"
+  # set the right prefix/lib directories
+  sed -e 's/prefix=\/usr/prefix=\/app\/.heroku\/python/' -e 's/\/x86_64-linux-gnu//' "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/x86_64-linux-gnu/pkgconfig/sqlite3.pc" > "$HEROKU_PYTHON_DIR/lib/pkgconfig/sqlite3.pc"
+  # need to point the libsqlite3.so to the stack image library for /usr/bin/ld -lsqlite3
+  SQLITE3_LIBFILE="/usr/lib/x86_64-linux-gnu/$(readlink -n "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/x86_64-linux-gnu/libsqlite3.so")"
+  ln -s "$SQLITE3_LIBFILE" "$HEROKU_PYTHON_DIR/lib/libsqlite3.so"
+  if [ -z "$HEADERS_ONLY" ]; then
+    mv "$HEROKU_PYTHON_DIR/sqlite3/usr/bin"/* "$HEROKU_PYTHON_DIR/bin/"
+  fi
+
+  # cleanup
+  rm -rf "$HEROKU_PYTHON_DIR/sqlite3/"
+  rm -rf "$HEROKU_PYTHON_DIR/apt/"
+}
+
+buildpack_sqlite3_install() {
+  HEROKU_PYTHON_DIR="$BUILD_DIR/.heroku/python"
+
+  SQLITE3_VERSION_FILE="$BUILD_DIR/.heroku/python-sqlite3-version"
+  if [ -f "$SQLITE3_VERSION_FILE" ]; then
+    INSTALLED_SQLITE3_VERSION=$(cat "$SQLITE3_VERSION_FILE")
+  fi
+
+  puts-step "Installing SQLite3"
+
+  if sqlite3_install "$BUILD_DIR/.heroku/python" ; then
+    mcount "success.python.sqlite3"
+  else
+    echo "Sqlite3 failed to install."
+    mcount "failure.python.sqlite3"
+  fi
+
+  mkdir -p "$CACHE_DIR/.heroku/"
+}

bin/test-compile

@@ -1,11 +1,13 @@
 #!/usr/bin/env bash
 
 # Syntax sugar.
-BIN_DIR=$(cd $(dirname $0); pwd) # absolute path
-source $BIN_DIR/utils
+BIN_DIR=$(cd "$(dirname "$0")" || return; pwd) # absolute path
 
-DISABLE_COLLECTSTATIC=1 "$(dirname ${0:-})/compile" "$1" "$2" "$3"
+# shellcheck source=bin/utils
+source "$BIN_DIR/utils"
 
-if [[ -f "$1/requirements-test.txt" ]]; then
-    /app/.heroku/python/bin/pip install -r "$1/requirements-test.txt" --exists-action=w --src=./.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | cleanup | indent
-fi
+# Locale support for Pipenv.
+export LC_ALL=C.UTF-8
+export LANG=C.UTF-8
+
+DISABLE_COLLECTSTATIC=1 INSTALL_TEST=1 "$(dirname "${0:-}")/compile" "$1" "$2" "$3"

bin/utils

@@ -1,6 +1,15 @@
+#!/usr/bin/env bash
 shopt -s extglob
+shopt -s nullglob
 
-if [ $(uname) == Darwin ]; then
+# The standard library.
+if [[ ! -f  /tmp/stdlib.sh ]]; then
+  curl --retry 3 -s https://lang-common.s3.amazonaws.com/buildpack-stdlib/v8/stdlib.sh > /tmp/stdlib.sh
+fi
+# shellcheck source=/dev/null
+source /tmp/stdlib.sh
+
+if [ "$(uname)" == Darwin ]; then
     sed() { command sed -l "$@"; }
 else
     sed() { command sed -u "$@"; }
@@ -11,46 +20,20 @@ indent() {
   sed "s/^/       /"
 }
 
+
 # Clean up pip output
 cleanup() {
   sed -e 's/\.\.\.\+/.../g' | sed -e '/already satisfied/Id' | sed -e '/No files were found to uninstall/Id' | sed -e '/Overwriting/Id' | sed -e '/python executable/Id' | sed -e '/no previously-included files/Id'
 }
 
-# Buildpack Indented line.
-puts-line() {
-  echo "       $@"
-}
-
 # Buildpack Steps.
 puts-step() {
-  echo "-----> $@"
+  echo "-----> $*"
 }
 
 # Buildpack Warnings.
 puts-warn() {
-  echo " !     $@"
-}
-
-# Buildpack Commands.
-puts-cmd() {
-  echo "     $ $@"
-}
-
-# Usage: $ set-env key value
-set-env() {
-  echo "export $1=$2" >> $PROFILE_PATH
-  echo "export $1=$2" >> $EXPORT_PATH
-}
-
-# Usage: $ set-default-env key value
-set-default-env() {
-  echo "export $1=\${$1:-$2}" >> $PROFILE_PATH
-  echo "export $1=\${$1:-$2}" >> $EXPORT_PATH
-}
-
-# Usage: $ un-set-env key
-un-set-env() {
-  echo "unset $1" >> $PROFILE_PATH
+  echo " !     $*"
 }
 
 # Does some serious copying.
@@ -69,42 +52,46 @@ deep-cp() {
   )
 }
 
-# Does some serious moving.
-deep-mv() {
-  deep-cp "$1" "$2"
-  deep-rm "$1"
+
+# Measure the size of the Python installation.
+measure-size() {
+  echo "$(du -s .heroku/python 2>/dev/null || echo 0) | awk '{print $1}')"
 }
 
-# Does some serious deleting.
-deep-rm() {
-  # subshell to avoid surprising caller with shopts.
-  (
-    shopt -s dotglob
-    rm -rf "$1"/!(.curlrc|.netrc|tmp|.|..)
-  )
+# Python version operator >
+version_gt() {
+  test "$(printf '%s\n' "$@" | sort -V | head -n 1)" != "$1";
 }
 
+# Python verison operator >=
+version_gte() {
+  if [ "$1" == "$2" ]; then
+    return 0
+  fi
 
-sub-env() {
-
-  WHITELIST=${2:-''}
-  BLACKLIST=${3:-'^(GIT_DIR|PYTHONHOME|LD_LIBRARY_PATH|LIBRARY_PATH|PATH)$'}
-
-  # Python-specific variables.
-  export PYHONHOME=$BUILD_DIR/.heroku/python
-  export PYTHONPATH=$BUILD_DIR/
-
-  (
-    if [ -d "$ENV_DIR" ]; then
-      for e in $(ls $ENV_DIR); do
-        echo "$e" | grep -E "$WHITELIST" | grep -qvE "$BLACKLIST" &&
-        export "$e=$(cat $ENV_DIR/$e)"
-        :
-      done
-    fi
-
-    $1
-
-  )
+  version_gt "$1" "$2"
 }
 
+# Check if Python 2
+python2_check() {
+  VERSION="$1"
+
+  version_gte "$VERSION" "python-2.7.0" && version_gt "python-3.0.0" "$VERSION"
+}
+
+# Check if Python 3
+python3_check() {
+  VERSION="$1"
+
+  version_gte "$VERSION" "python-3.0.0" && version_gt "python-4.0.0" "$VERSION"
+}
+
+# Check if Python version needs to install SQLite3
+python_sqlite3_check() {
+  VERSION="$1"
+  MIN_PYTHON_3="python-3.5.6"
+  MIN_PYTHON_2="python-2.7.15"
+
+  ( python2_check "$VERSION" && version_gte "$VERSION" "$MIN_PYTHON_2" ) \
+    || ( python3_check "$VERSION" && version_gte "$VERSION" "$MIN_PYTHON_3" )
+}

bin/warnings

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 shopt -s extglob
 
 old-platform() {
@@ -7,6 +8,7 @@ old-platform() {
     puts-warn "This caused the security warning you saw above during the 'pip install' step."
     puts-warn "We recommend '$RECOMMENDED_PYTHON_VERSION', which you can specify in a 'runtime.txt' file."
     puts-warn "  -- Much Love, Heroku."
+    mcount 'warnings.python.old'
   fi
 }
 
@@ -16,6 +18,7 @@ pylibmc-missing() {
     puts-warn "Hello! There was a problem with your build related to libmemcache."
     puts-warn "The Python library 'pylibmc' must be explicitly specified in 'requirements.txt' in order to build correctly."
     puts-warn "Once you do that, everything should work as expected.   -- Much Love, Heroku."
+    mcount 'warnings.libmemcache'
   fi
 }
 
@@ -27,6 +30,7 @@ scipy-included() {
     puts-warn "There is, however, a buildpack available that makes it possible to use it on Heroku."
     puts-warn "You can learn more here:  https://devcenter.heroku.com/articles/python-c-deps"
     puts-warn "Sorry for the inconvenience.   -- Much Love, Heroku."
+    mcount 'warnings.scipy'
   fi
 }
 
@@ -37,6 +41,18 @@ distribute-included() {
     puts-warn "This library is automatically installed by Heroku and shouldn't be in"
     puts-warn "Your requirements.txt file. This can cause unexpected behavior."
     puts-warn "  -- Much Love, Heroku."
+    mcount 'warnings.distribute'
+  fi
+}
+
+six-included() {
+  if grep -qi 'Running setup.py install for six' "$WARNINGS_LOG"; then
+    echo
+    puts-warn "Hello! Your requirements.txt file contains the six package."
+    puts-warn "This library is automatically installed by Heroku and shouldn't be in"
+    puts-warn "Your requirements.txt file. This can cause unexpected behavior."
+    puts-warn "  -- Much Love, Heroku."
+    mcount 'warnings.six'
   fi
 }
 
@@ -45,5 +61,6 @@ show-warnings() {
   pylibmc-missing
   scipy-included
   distribute-included
+  six-included
 }
 

buildpack.toml

@@ -0,0 +1,13 @@
+[buildpack]
+name = "Python"
+
+  [publish.Ignore]
+  files = [
+    "test/",
+    ".gitignore",
+    ".dockerignore",
+    ".github/",
+    "Dockerfile",
+    "Pipfile",
+    "Pipfile.lock"
+  ]

builds/README.md

@@ -1,31 +1,57 @@
 # Python Buildpack Binaries
 
+## Building the Docker Images
 
-To get started with it, create an app on Heroku inside a clone of this repository, and set your S3 config vars:
+**After every change to your formulae, perform the following** from the root of the Git repository (not from `builds/`) to rebuild the images for each stack:
 
-    $ heroku create --buildpack https://github.com/heroku/heroku-buildpack-python#not-heroku
-    $ heroku config:set WORKSPACE_DIR=builds
-    $ heroku config:set AWS_ACCESS_KEY_ID=<your_aws_key>
-    $ heroku config:set AWS_SECRET_ACCESS_KEY=<your_aws_secret>
-    $ heroku config:set S3_BUCKET=<your_s3_bucket_name>
+    $ docker build --pull --tag heroku-python-build-cedar-14 --file $(pwd)/builds/cedar-14.Dockerfile .
+    $ docker build --pull --tag heroku-python-build-heroku-16 --file $(pwd)/builds/heroku-16.Dockerfile .
+    $ docker build --pull --tag heroku-python-build-heroku-18 --file $(pwd)/builds/heroku-18.Dockerfile .
 
+## Using the Image
 
-Then, shell into an instance and run a build by giving the name of the formula inside `builds`:
+You can e.g. `bash` into each of the images you built using their tag:
 
-    $ heroku run bash
-    Running `bash` attached to terminal... up, run.6880
-    ~ $ bob build runtimes/python-2.7.6
+    docker run --rm -ti heroku-python-build-cedar-14 bash
+    docker run --rm -ti heroku-python-build-heroku-16 bash
+    docker run --rm -ti heroku-python-build-heroku-18 bash
 
-    Fetching dependencies... found 2:
-      - libraries/sqlite
+You then have a shell where you can run `bob build`, `bob deploy`, and so forth. You can of course also invoke these programs directly with `docker run`:
 
-    Building formula runtimes/python-2.7.6:
-        === Building Python 2.7.6
-        Fetching Python v2.7.6 source...
-        Compiling...
+    docker run --rm -ti heroku-python-build-heroku-18 bob build runtimes/python-2.7.15
 
-If this works, run `bob deploy` instead of `bob build` to have the result uploaded to S3 for you.
+In order to `bob deploy`, AWS credentials must be set up, as well as name and prefix of your custom S3 bucket (unless you're deploying to the Heroku production buckets that are pre-defined in each `Dockerfile`); see next section for details.
 
-To speed things up drastically, it'll usually be a good idea to `heroku run bash --size PX` instead.
+## Configuration
 
-Enjoy :)
+File `dockerenv.default` contains a list of required env vars; most of these have default values defined in `Dockerfile`. You can copy this file to a location outside the buildpack and modify it with the values you desire and pass its location with `--env-file`, or pass the env vars to `docker run` using `--env`.
+
+Out of the box, each `Dockerfile` has the correct values predefined for `S3_BUCKET`, `S3_PREFIX`, and `S3_REGION`. If you're building your own packages, you'll likely want to change `S3_BUCKET` and `S3_PREFIX` to match your info. Instead of setting `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` into that file, you may also pass them to `docker run` through the environment, or explicitly using `--env`, in order to prevent accidental commits of credentials.
+
+### Passing AWS credentials to the container
+
+If you want to deploy packages and thus need to pass `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY`, you can either pass them explicitly, through your environment, or through an env file.
+
+#### Passing credentials explicitly
+
+    docker run --rm -ti -e AWS_ACCESS_KEY_ID=... -e AWS_SECRET_ACCESS_KEY=... heroku-python-build-heroku-18 bash
+
+#### Passing credentials through  the environment
+
+The two environment variables `AWS_ACCESS_KEY_ID`and `AWS_SECRET_ACCESS_KEY` are defined in `builds/dockerenv.default`, without values. This will cause Docker to "forward" values for these variables from the current environment, so you can pass them in:
+
+    AWS_ACCESS_KEY_ID=... AWS_SECRET_ACCESS_KEY=... docker run --rm -ti --env-file=builds/dockerenv.default heroku-python-build-heroku-18 bash
+
+or
+
+    export AWS_ACCESS_KEY_ID=...
+    export AWS_SECRET_ACCESS_KEY=...
+    docker run --rm -ti --env-file=builds/dockerenv.default heroku-python-build-heroku-18 bash
+
+#### Passing credentials through a separate env file
+
+This method is the easiest for users who want to build packages in their own S3 bucket, as they will have to adjust the `S3_BUCKET` and `S3_PREFIX` environment variable values anyway from their default values.
+
+For this method, it is important to keep the credentials file in a location outside the buildpack, so that your credentials aren't accidentally committed. Copy `builds/dockerenv.default` **to a safe location outside the buildpack directory**, and insert your values for `AWS_ACCESS_KEY_ID`and `AWS_SECRET_ACCESS_KEY`.
+
+    docker run --rm -ti --env-file=../SOMEPATHOUTSIDE/s3.env heroku-python-build-heroku-18 bash

builds/cedar-14.Dockerfile

@@ -0,0 +1,15 @@
+FROM heroku/cedar:14
+
+WORKDIR /app
+ENV WORKSPACE_DIR="/app/builds" \
+    S3_BUCKET="lang-python" \
+    S3_PREFIX="cedar-14/" \
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="cedar-14"
+
+RUN apt-get update && apt-get install -y python-pip libsqlite3-dev realpath && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt /app/
+RUN pip install -r /app/requirements.txt
+
+COPY . /app

builds/dockerenv.default

@@ -0,0 +1,5 @@
+AWS_ACCESS_KEY_ID
+AWS_SECRET_ACCESS_KEY
+S3_BUCKET
+S3_PREFIX
+S3_REGION

builds/heroku-16.Dockerfile

@@ -0,0 +1,15 @@
+FROM heroku/heroku:16-build
+
+WORKDIR /app
+ENV WORKSPACE_DIR="/app/builds" \
+    S3_BUCKET="lang-python" \
+    S3_PREFIX="heroku-16/" \
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="heroku-16"
+
+RUN apt-get update && apt-get install -y python-pip libsqlite3-dev && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt /app/
+RUN pip install --disable-pip-version-check --no-cache-dir -r /app/requirements.txt
+
+COPY . /app

builds/heroku-18.Dockerfile

@@ -0,0 +1,15 @@
+FROM heroku/heroku:18-build
+
+WORKDIR /app
+ENV WORKSPACE_DIR="/app/builds" \
+    S3_BUCKET="lang-python" \
+    S3_PREFIX="heroku-18/" \
+    DEBIAN_FRONTEND=noninteractive \
+    STACK="heroku-18"
+
+RUN apt-get update && apt-get install --no-install-recommends -y python-pip-whl=9.0.1-2 python-pip=9.0.1-2 python-setuptools python-wheel libsqlite3-dev && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt /app/
+RUN pip install --disable-pip-version-check --no-cache-dir -r /app/requirements.txt
+
+COPY . /app

builds/libraries/sqlite

@@ -3,7 +3,7 @@
 
 OUT_PREFIX=$1
 
-echo "Building SQLite..."
+echo "Building SQLite…"
 
 
 SOURCE_TARBALL='https://www.sqlite.org/sqlite-autoconf-3070900.tar.gz'

builds/libraries/vendor/gdal

@@ -8,16 +8,17 @@ export PATH="/app/.heroku/python/bin/:$PATH"
 hash -r
 
 
-echo "Building gdal..."
+echo "Building gdal…"
 
-SOURCE_TARBALL='http://download.osgeo.org/gdal/1.11.1/gdal-1.11.1.tar.gz'
+VERSION="2.2.1"
+SOURCE_TARBALL="http://download.osgeo.org/gdal/${VERSION}/gdal-${VERSION}.tar.gz"
 
 curl -L $SOURCE_TARBALL | tar zx
 
-cd gdal-1.11.1
+pushd "gdal-${VERSION}"
 ./configure --prefix=$OUT_PREFIX --enable-static=no  &&
 make
 make install
 
 # Cleanup
-cd ..
+popd

builds/libraries/vendor/geos

@@ -8,16 +8,18 @@ export PATH="/app/.heroku/python/bin/:$PATH"
 hash -r
 
 
-echo "Building geos..."
+echo "Building geos…"
 
-SOURCE_TARBALL='http://download.osgeo.org/geos/geos-3.4.3.tar.bz2'
+VERSION=3.6.2
+
+SOURCE_TARBALL="http://download.osgeo.org/geos/geos-${VERSION}.tar.bz2"
 
 curl -L $SOURCE_TARBALL | tar xj
 
-cd geos-3.4.3
+pushd "geos-${VERSION}"
 ./configure --prefix=$OUT_PREFIX --enable-static=no &&
 make
 make install
 
 # Cleanup
-cd ..
+popd

builds/libraries/vendor/libffi

@@ -1,28 +0,0 @@
-#!/usr/bin/env bash
-# Build Path: /app/.heroku/vendor/
-
-OUT_PREFIX=$1
-
-# Skip the build for heroku-16.
-if [[ $S3_PREFIX == "heroku-16" ]]; then
-    exit 0
-fi
-
-# Use new path, containing autoconf.
-export PATH="/app/.heroku/python/bin/:$PATH"
-hash -r
-
-
-echo "Building libffi..."
-
-SOURCE_TARBALL='ftp://sourceware.org/pub/libffi/libffi-3.1.tar.gz'
-
-curl -L $SOURCE_TARBALL | tar x
-
-cd libffi-3.1
-./configure --prefix=$OUT_PREFIX --disable-static &&
-make
-make install
-
-# Cleanup
-cd ..

builds/libraries/vendor/libmemcache

@@ -3,9 +3,9 @@
 
 OUT_PREFIX=$1
 
-# Skip the build for heroku-16.
-if [[ $S3_PREFIX == "heroku-16" ]]; then
-    exit 0
+if [[ $S3_PREFIX != "cedar-14" ]]; then
+    echo "libmemcached only needs to be built for cedar-14, since newer stacks include it in the base image"
+    exit 1
 fi
 
 # fail hard
@@ -20,7 +20,7 @@ dep_archive_name=${dep_dirname}.tar.gz
 dep_url=https://launchpad.net/libmemcached/1.0/${dep_version}/+download/${dep_archive_name}
 
 # SASL Support.
-echo "-----> Building cyrus-sasl 2.1.26..."
+echo "-----> Building cyrus-sasl 2.1.26…"
 
 curl -LO ftp://ftp.cyrusimap.org/cyrus-sasl/cyrus-sasl-2.1.26.tar.gz
 # FTP doesn't play well with piping into tar xz
@@ -33,7 +33,7 @@ make -s -j 9
 make install -s
 popd
 
-echo "-----> Building libmemcached ${dep_version}..."
+echo "-----> Building libmemcached ${dep_version}…"
 
 curl -L ${dep_url} | tar xz
 pushd ${dep_dirname}

builds/libraries/vendor/proj

@@ -8,16 +8,17 @@ export PATH="/app/.heroku/python/bin/:$PATH"
 hash -r
 
 
-echo "Building gdal..."
+echo "Building gdal…"
 
-SOURCE_TARBALL='http://download.osgeo.org/proj/proj-4.8.0.tar.gz'
+VERSION=4.9.3
+SOURCE_TARBALL="http://download.osgeo.org/proj/proj-${VERSION}.tar.gz"
 
 curl -L $SOURCE_TARBALL | tar zx
 
-cd proj-4.8.0
-./configure --prefix=$OUT_PREFIX --enable-static=no &&
+pushd "proj-${VERSION}"
+./configure --prefix=$OUT_PREFIX --enable-static=no
 make
 make install
 
 # Cleanup
-cd ..
+popd

builds/runtimes/pypy

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# fail hard
+set -o pipefail
+# fail harder
+set -eu
+
+OUT_PREFIX=$1
+
+dep_formula=${0#$WORKSPACE_DIR/} # this is the original script, e.g. pypy-5.3.1
+dep_name=$(basename $BASH_SOURCE) # this is us
+dep_version=${dep_formula##*"/${dep_name}-"} # "subtract" our name from full version name
+dep_package=${dep_name}2-v${dep_version} # it's always "pypy2-…"
+dep_dirname=${dep_package}-linux64
+dep_archive_name=${dep_dirname}.tar.bz2
+dep_url=https://bitbucket.org/pypy/pypy/downloads/${dep_archive_name}
+
+echo "Building PyPy…"
+
+curl -L "${dep_url}" | tar jx -C "${OUT_PREFIX}" --strip-components 1 # extract to $OUT_PREFIX, drop the first directory level, which is the archive name
+
+ln "$OUT_PREFIX/bin/pypy" "$OUT_PREFIX/bin/python"

builds/runtimes/pypy-5.3.1

@@ -2,13 +2,4 @@
 # Build Path: /app/.heroku/python/
 # Build Deps: libraries/sqlite
 
-# NOTICE: This formula only works for the cedar-14 stack, not cedar.
-
-OUT_PREFIX=$1
-
-echo "Building PyPy..."
-SOURCE_TARBALL='https://bitbucket.org/pypy/pypy/downloads/pypy2-v5.3.1-linux64.tar.bz2'
-curl -L $SOURCE_TARBALL | tar jx
-cp -R pypy2-v5.3.1-linux64/* $OUT_PREFIX
-
-ln $OUT_PREFIX/bin/pypy $OUT_PREFIX/bin/python
+source $(dirname $0)/pypy

builds/runtimes/pypy-5.6.0

@@ -2,13 +2,4 @@
 # Build Path: /app/.heroku/python/
 # Build Deps: libraries/sqlite
 
-# NOTICE: This formula only works for the cedar-14 stack, not cedar.
-
-OUT_PREFIX=$1
-
-echo "Building PyPy..."
-SOURCE_TARBALL='https://bitbucket.org/pypy/pypy/downloads/pypy2-v5.6.0-linux64.tar.bz2'
-curl -L $SOURCE_TARBALL | tar jx
-cp -R pypy2-v5.6.0-linux64/* $OUT_PREFIX
-
-ln $OUT_PREFIX/bin/pypy $OUT_PREFIX/bin/python
+source $(dirname $0)/pypy

builds/runtimes/pypy-5.7.0

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+# Build Deps: libraries/sqlite
+
+source $(dirname $0)/pypy

builds/runtimes/pypy-5.7.1

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+# Build Deps: libraries/sqlite
+
+source $(dirname $0)/pypy

builds/runtimes/pypy-5.8.0

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+# Build Deps: libraries/sqlite
+
+source $(dirname $0)/pypy

builds/runtimes/pypy2.7

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+# fail hard
+set -o pipefail
+# fail harder
+set -eu
+
+OUT_PREFIX=$1
+
+dep_formula=${0#$WORKSPACE_DIR/} # this is the original script, e.g. pypy-5.3.1
+dep_name=$(basename $BASH_SOURCE) # this is us
+dep_version=${dep_formula##*"/${dep_name}-"} # "subtract" our name from full version name
+dep_package=${dep_name}-v${dep_version} # it's always "pypy2-…"
+dep_dirname=${dep_package}-linux64
+dep_archive_name=${dep_dirname}.tar.bz2
+dep_url=https://bitbucket.org/pypy/pypy/downloads/${dep_archive_name}
+
+echo "Building PyPy…"
+echo "${dep_url}"
+
+curl -L "${dep_url}" | tar jx -C "${OUT_PREFIX}" --strip-components 1 # extract to $OUT_PREFIX, drop the first directory level, which is the archive name
+
+ln "$OUT_PREFIX/bin/pypy" "$OUT_PREFIX/bin/python"

builds/runtimes/pypy2.7-7.2.0

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/pypy2.7

builds/runtimes/pypy2.7-7.3.1

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/pypy2.7

builds/runtimes/pypy3

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# fail hard
+set -o pipefail
+# fail harder
+set -eu
+
+OUT_PREFIX=$1
+
+dep_formula=${0#$WORKSPACE_DIR/} # this is the original script, e.g. pypy-5.3.1
+dep_name=$(basename $BASH_SOURCE) # this is us
+dep_version=${dep_formula##*"/${dep_name}-"} # "subtract" our name from full version name
+dep_package=${dep_name}${dep_version_prefix:-}-v${dep_version}${dep_version_suffix:-}
+dep_dirname=${dep_package}-linux64
+dep_archive_name=${dep_dirname}.tar.bz2
+dep_url=https://bitbucket.org/pypy/pypy/downloads/${dep_archive_name}
+
+echo "Building PyPy3…"
+
+curl -L "${dep_url}" | tar jx -C "${OUT_PREFIX}" --strip-components 1 # extract to $OUT_PREFIX, drop the first directory level, which is the archive name
+
+ln "$OUT_PREFIX/bin/pypy3" "$OUT_PREFIX/bin/python"

builds/runtimes/pypy3-2.4.0

@@ -2,13 +2,4 @@
 # Build Path: /app/.heroku/python/
 # Build Deps: libraries/sqlite
 
-# NOTICE: This formula only works for the cedar-14 stack, not cedar.
-
-OUT_PREFIX=$1
-
-echo "Building PyPy..."
-SOURCE_TARBALL='https://bitbucket.org/pypy/pypy/downloads/pypy3-2.4.0-linux64.tar.bz2'
-curl -L $SOURCE_TARBALL | tar jx
-cp -R pypy3-2.4.0-linux64/* $OUT_PREFIX
-
-ln $OUT_PREFIX/bin/pypy3 $OUT_PREFIX/bin/python
+source $(dirname $0)/pypy3

builds/runtimes/pypy3-5.5.0

@@ -2,13 +2,7 @@
 # Build Path: /app/.heroku/python/
 # Build Deps: libraries/sqlite
 
-# NOTICE: This formula only works for the cedar-14 stack, not cedar.
-
-OUT_PREFIX=$1
-
-echo "Building PyPy..."
-SOURCE_TARBALL='https://bitbucket.org/pypy/pypy/downloads/pypy3.3-v5.5.0-alpha-linux64.tar.bz2'
-curl -L $SOURCE_TARBALL | tar jx
-cp -R pypy3-v5.5.0-linux64/* $OUT_PREFIX
-
-ln $OUT_PREFIX/bin/pypy3 $OUT_PREFIX/bin/python
+# version pypy3-5.5.0 is really called pypy3.3-v5.5.0-alpha
+dep_version_prefix=".3"
+dep_version_suffix="-alpha"
+source $(dirname $0)/pypy3

builds/runtimes/pypy3-5.7.1

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+# Build Deps: libraries/sqlite
+
+source $(dirname $0)/pypy3

builds/runtimes/pypy3-5.8.0

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+# Build Deps: libraries/sqlite
+
+source $(dirname $0)/pypy3

builds/runtimes/pypy3.6

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+# fail hard
+set -o pipefail
+# fail harder
+set -eu
+
+OUT_PREFIX=$1
+
+dep_formula=${0#$WORKSPACE_DIR/} # this is the original script, e.g. pypy-5.3.1
+dep_name=$(basename $BASH_SOURCE) # this is us
+dep_version=${dep_formula##*"/${dep_name}-"} # "subtract" our name from full version name
+dep_package=${dep_name}${dep_version_prefix:-}-v${dep_version}${dep_version_suffix:-}
+dep_dirname=${dep_package}-linux64
+dep_archive_name=${dep_dirname}.tar.bz2
+dep_url=https://bitbucket.org/pypy/pypy/downloads/${dep_archive_name}
+
+echo "Building PyPy3…"
+echo "${dep_url}"
+
+curl -L "${dep_url}" | tar jx -C "${OUT_PREFIX}" --strip-components 1 # extract to $OUT_PREFIX, drop the first directory level, which is the archive name
+
+ln "$OUT_PREFIX/bin/pypy3" "$OUT_PREFIX/bin/python"

builds/runtimes/pypy3.6-7.2.0

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/pypy3.6

builds/runtimes/pypy3.6-7.3.1

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/pypy3.6

builds/runtimes/python-2.7.10

@@ -1,15 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
 
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/2.7.10/Python-2.7.10.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-2.7.10 src
-cd src
-
-./configure --prefix=$OUT_PREFIX  --with-ensurepip=no
-make
-make install
+source $(dirname $0)/python2

builds/runtimes/python-2.7.11

@@ -1,15 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
 
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/2.7.11/Python-2.7.11.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-2.7.11 src
-cd src
-
-./configure --prefix=$OUT_PREFIX  --with-ensurepip=no
-make
-make install
+source $(dirname $0)/python2

builds/runtimes/python-2.7.12

@@ -1,15 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
 
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/2.7.12/Python-2.7.12.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-2.7.12 src
-cd src
-
-./configure --prefix=$OUT_PREFIX  --with-ensurepip=no
-make
-make install
+source $(dirname $0)/python2

builds/runtimes/python-2.7.13

@@ -1,15 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
 
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/2.7.13/Python-2.7.13.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-2.7.13 src
-cd src
-
-./configure --prefix=$OUT_PREFIX  --enable-unicode=ucs4 --with-ensurepip=no
-make
-make install
+source $(dirname $0)/python2

builds/runtimes/python-2.7.14

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python2

builds/runtimes/python-2.7.15

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python2

builds/runtimes/python-2.7.16

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python2

builds/runtimes/python-2.7.17

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+OUT_PREFIX=$1
+BIN_DIR="$(cd "$(dirname "$0")"/../.. || exit; pwd)/bin"
+export BIN_DIR
+
+# shellcheck source=bin/utils
+source "$BIN_DIR/steps/sqlite3"
+
+sqlite3_version
+echo "Setting up SQLite3 Headers for $SQLITE3_VERSION"
+sqlite3_install "$OUT_PREFIX" "$SQLITE3_VERSION" 1
+
+echo "Building Python…"
+SOURCE_TARBALL='https://python.org/ftp/python/2.7.17/Python-2.7.17.tgz'
+curl -L $SOURCE_TARBALL | tar xz
+mv Python-2.7.17 src
+cd src
+
+./configure --prefix=$OUT_PREFIX  --enable-unicode=ucs4 --with-ensurepip=no
+make
+make install
+
+# Remove unneeded test directories, similar to the official Docker Python images:
+# https://github.com/docker-library/python
+find "${OUT_PREFIX}" \( -type d -a \( -name test -o -name tests \) \) -exec rm -rf '{}' +

builds/runtimes/python-2.7.18

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+OUT_PREFIX=$1
+BIN_DIR="$(cd "$(dirname "$0")"/../.. || exit; pwd)/bin"
+export BIN_DIR
+
+# shellcheck source=bin/utils
+source "$BIN_DIR/steps/sqlite3"
+
+sqlite3_version
+echo "Setting up SQLite3 Headers for $SQLITE3_VERSION"
+sqlite3_install "$OUT_PREFIX" "$SQLITE3_VERSION" 1
+
+echo "Building Python…"
+SOURCE_TARBALL='https://python.org/ftp/python/2.7.18/Python-2.7.18.tgz'
+curl -L $SOURCE_TARBALL | tar xz
+mv Python-2.7.18 src
+cd src
+
+./configure --prefix=$OUT_PREFIX  --enable-unicode=ucs4 --with-ensurepip=no
+make
+make install
+
+# Remove unneeded test directories, similar to the official Docker Python images:
+# https://github.com/docker-library/python
+find "${OUT_PREFIX}" \( -type d -a \( -name test -o -name tests \) \) -exec rm -rf '{}' +

builds/runtimes/python-2.7.9

@@ -1,15 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
 
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/2.7.9/Python-2.7.9.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-2.7.9 src
-cd src
-
-./configure --prefix=$OUT_PREFIX  --with-ensurepip=no
-make
-make install
+source $(dirname $0)/python2

builds/runtimes/python-3.4.10

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+OUT_PREFIX=$1
+BIN_DIR="$(cd "$(dirname "$0")"/../.. || exit; pwd)/bin"
+export BIN_DIR
+
+# shellcheck source=bin/utils
+source "$BIN_DIR/steps/sqlite3"
+
+sqlite3_version
+echo "Setting up SQLite3 Headers for $SQLITE3_VERSION"
+sqlite3_install "$OUT_PREFIX" "$SQLITE3_VERSION" 1
+
+echo "Building Python…"
+SOURCE_TARBALL='https://python.org/ftp/python/3.7.2/Python-3.7.2.tgz'
+curl -L $SOURCE_TARBALL | tar xz
+mv Python-3.7.2 src
+cd src
+
+./configure --prefix=$OUT_PREFIX --with-ensurepip=no
+make
+make install
+
+# Remove unneeded test directories, similar to the official Docker Python images:
+# https://github.com/docker-library/python
+find "${OUT_PREFIX}" \( -type d -a \( -name test -o -name tests \) \) -exec rm -rf '{}' +
+
+# Remove spare /
+LOCATION=${OUT_PREFIX%?}
+
+ln $LOCATION/bin/python3 $LOCATION/bin/python

builds/runtimes/python-3.4.9

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+OUT_PREFIX=$1
+BIN_DIR="$(cd "$(dirname "$0")"/../.. || exit; pwd)/bin"
+export BIN_DIR
+
+# shellcheck source=bin/utils
+source "$BIN_DIR/steps/sqlite3"
+
+sqlite3_version
+echo "Setting up SQLite3 Headers for $SQLITE3_VERSION"
+sqlite3_install "$OUT_PREFIX" "$SQLITE3_VERSION" 1
+
+echo "Building Python…"
+SOURCE_TARBALL='https://python.org/ftp/python/3.4.9/Python-3.4.9.tgz'
+curl -L $SOURCE_TARBALL | tar xz
+mv Python-3.4.9 src
+cd src
+
+./configure --prefix=$OUT_PREFIX --with-ensurepip=no
+make
+make install
+
+# Remove unneeded test directories, similar to the official Docker Python images:
+# https://github.com/docker-library/python
+find "${OUT_PREFIX}" \( -type d -a \( -name test -o -name tests \) \) -exec rm -rf '{}' +
+
+# Remove spare /
+LOCATION=${OUT_PREFIX%?}
+
+ln $LOCATION/bin/python3 $LOCATION/bin/python

builds/runtimes/python-3.5.0

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.1

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.2

@@ -1,18 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
-
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/3.5.2/Python-3.5.2.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-3.5.2 src
-cd src
-
-./configure --prefix=$OUT_PREFIX --with-ensurepip=no
-make
-make install
-
-# ln $OUT_PREFIX/bin/python3 $OUT_PREFIX/bin/python
 
+source $(dirname $0)/python3

builds/runtimes/python-3.5.3

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.4

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.5

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.6

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.7

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.5.9

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.0

@@ -1,18 +1,4 @@
 #!/usr/bin/env bash
 # Build Path: /app/.heroku/python/
-# Build Deps: libraries/sqlite
-
-OUT_PREFIX=$1
-
-echo "Building Python..."
-SOURCE_TARBALL='https://python.org/ftp/python/3.6.0/Python-3.6.0.tgz'
-curl -L $SOURCE_TARBALL | tar xz
-mv Python-3.6.0 src
-cd src
-
-./configure --prefix=$OUT_PREFIX --with-ensurepip=no
-make
-make install
-
-ln $OUT_PREFIX/bin/python3 $OUT_PREFIX/bin/python
 
+source $(dirname $0)/python3

builds/runtimes/python-3.6.1

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.10

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.11

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.2

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.3

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.4

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.5

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

builds/runtimes/python-3.6.6

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3