From bdcf7cc40d17e307882291566e3ba577b02760e4 Mon Sep 17 00:00:00 2001
From: Kenneth Reitz <me@kennethreitz.org>
Date: Tue, 16 Jan 2018 09:54:14 -0500
Subject: [PATCH] lazy load modules

---
 pipenv/cli.py                      | 10 +++++
 pipenv/vendor/lazyload/__init__.py | 61 ++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 pipenv/vendor/lazyload/__init__.py

diff --git a/pipenv/cli.py b/pipenv/cli.py
index 81bf29ec..dc3294ef 100644
--- a/pipenv/cli.py
+++ b/pipenv/cli.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+
 import contextlib
 import codecs
 import os
@@ -10,6 +11,15 @@ import tempfile
 from glob import glob
 import json as simplejson
 
+import lazyload
+for module in [
+    'urllib3', 'background', 'dotenv', 'delegator', 'pexpect',
+    'requests', 'pip', 'pipfile', 'pipdeptree', 'requirements',
+    'semver', 'flake8', 'pipreqs', 'blindspin', 'click_didyoumean',
+    '.project', '.utils'
+]:
+    lazyload.make_lazy(module)
+
 import urllib3
 import background
 import click
diff --git a/pipenv/vendor/lazyload/__init__.py b/pipenv/vendor/lazyload/__init__.py
new file mode 100644
index 00000000..aeb0753e
--- /dev/null
+++ b/pipenv/vendor/lazyload/__init__.py
@@ -0,0 +1,61 @@
+import sys
+from types import ModuleType
+
+
+class _LazyModuleMarker(object):
+    """
+    A marker to indicate a LazyModule type.
+    Allows us to check module's with `isinstance(mod, _LazyModuleMarker)`
+    to know if the module is lazy.
+    """
+    pass
+
+
+class NonLocal(object):
+    """
+    Simulates nonlocal keyword in Python 2
+    """
+    __slots__ = ['value']
+
+    def __init__(self, value):
+        self.value = value
+
+
+def make_lazy(module_path):
+    """
+    Mark that this module should not be imported until an
+    attribute is needed off of it.
+    """
+    sys_modules = sys.modules  # cache in the locals
+
+    # store our 'instance' data in the closure.
+    module = NonLocal(None)
+
+    class LazyModule(_LazyModuleMarker):
+        """
+        A standin for a module to prevent it from being imported
+        """
+        def __mro__(self):
+            """
+            Override the __mro__ to fool `isinstance`.
+            """
+            # We don't use direct subclassing because `ModuleType` has an
+            # incompatible metaclass base with object (they are both in c)
+            # and we are overridding __getattribute__.
+            # By putting a __mro__ method here, we can pass `isinstance`
+            # checks without ever invoking our __getattribute__ function.
+            return (LazyModule, ModuleType)
+
+        def __getattribute__(self, attr):
+            """
+            Override __getattribute__ to hide the implementation details.
+            """
+            if module.value is None:
+                del sys_modules[module_path]
+                module.value = __import__(module_path)
+
+                sys_modules[module_path] = __import__(module_path)
+
+            return getattr(module.value, attr)
+
+    sys_modules[module_path] = LazyModule()