Merge lp:~ajkavanagh/charm-helpers/fix-path-mangling-lp1540299 into lp:charm-helpers

[Alex Kavanagh]

Mod to charmhelpers.contrib.python.packages to stop importing pip from adding wheels to the path when it is included as an import in another file. This is to prevent the side-effect of unintentionally including an updated module over an expected system package. The pip_execute() command still causes the path/wheels to be included for the duration of the pip_execute() command only (the path is restored after the pip_execute()) finishes.

[Liam Young (gnuoy)]

Approved, thanks for the fix

review: Approve

=== modified file 'charmhelpers/contrib/python/packages.py'
--- charmhelpers/contrib/python/packages.py	2015-11-03 19:40:58 +0000
+++ charmhelpers/contrib/python/packages.py	2016-02-02 13:51:49 +0000
@@ -19,20 +19,35 @@
 
 import os
 import subprocess
+import sys
 
 from charmhelpers.fetch import apt_install, apt_update
 from charmhelpers.core.hookenv import charm_dir, log
 
-try:
-    from pip import main as pip_execute
-except ImportError:
-    apt_update()
-    apt_install('python-pip')
-    from pip import main as pip_execute
-
 __author__ = "Jorge Niedbalski <[e-mail]>"
 
 
+def pip_execute(*args, **kwargs):
+    """Overriden pip_execute() to stop sys.path being changed.
+
+    The act of importing main from the pip module seems to cause add wheels
+    from the /usr/share/python-wheels which are installed by various tools.
+    This function ensures that sys.path remains the same after the call is
+    executed.
+    """
+    try:
+        _path = sys.path
+        try:
+            from pip import main as _pip_execute
+        except ImportError:
+            apt_update()
+            apt_install('python-pip')
+            from pip import main as _pip_execute
+        _pip_execute(*args, **kwargs)
+    finally:
+        sys.path = _path
+
+
 def parse_options(given, available):
     """Given a set of options, check if available"""
     for key, value in sorted(given.items()):