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Ed Morley
7279ddded8
Previously the pip/setuptools/wheel install step was skipped so long as Python hadn't just been clean installed (ie so long as not a new app, emptied cache, Python upgrade, stack change) and pip was the expected version. This meant that setuptool/wheel could be the wrong version (or even just not installed at all), and this would not be corrected. Now, we now use pip itself to determine whether the installed packages are up to date, since parsing pip's output is fragile (eg #1003) and would be tedious given there would be three packages to check. Unfortunately `get-pip.py` uses `--force-reinstall` which means performing this step every time is not the no-op it would otherwise be, but this will be resolved by switching away from `get-pip.py` in the next commit. Fixes #1000. Fixes #1003. Closes #999.
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.