From 526db7293aa439df63364a4dca7850670a9fd8dc Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@edx.org>
Date: Tue, 23 Feb 2016 12:52:18 -0500
Subject: [PATCH] A better way to manage the Python packages to uninstall.

---
 pavelib/prereqs.py | 72 +++++++++++++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 27 deletions(-)

diff --git a/pavelib/prereqs.py b/pavelib/prereqs.py
index cb0d60d62e..c7e25c6cb2 100644
--- a/pavelib/prereqs.py
+++ b/pavelib/prereqs.py
@@ -5,11 +5,12 @@ Install Python and Node prerequisites.
 from distutils import sysconfig
 import hashlib
 import os
+import re
+import sys
 
 from paver.easy import sh, task
 
 from .utils.envs import Env
-import sys
 
 
 PREREQS_STATE_DIR = os.getenv('PREREQ_CACHE_DIR', Env.REPO_ROOT / '.prereqs_cache')
@@ -151,6 +152,16 @@ def install_node_prereqs():
     prereq_cache("Node prereqs", ["package.json"], node_prereqs_installation)
 
 
+# To add a package to the uninstall list, just add it to this list! No need
+# to touch any other part of this file.
+PACKAGES_TO_UNINSTALL = [
+    "South",                        # Because it interferes with Django 1.8 migrations.
+    "edxval",                       # Because it was bork-installed somehow.
+    "django-storages",
+    "django-oauth2-provider",       # Because now it's called edx-django-oauth2-provider.
+]
+
+
 @task
 def uninstall_python_packages():
     """
@@ -162,14 +173,18 @@ def uninstall_python_packages():
     them.
 
     """
-    # So that we don't constantly uninstall things, use a version number of the
-    # uninstallation needs.  Check it, and skip this if we're up to date.
-    expected_version = 3
-    state_file_path = os.path.join(PREREQS_STATE_DIR, "python_uninstall_version.txt")
+    # So that we don't constantly uninstall things, use a hash of the packages
+    # to be uninstalled.  Check it, and skip this if we're up to date.
+    hasher = hashlib.sha1()
+    hasher.update(repr(PACKAGES_TO_UNINSTALL))
+    expected_version = hasher.hexdigest()
+    state_file_path = os.path.join(PREREQS_STATE_DIR, "Python_uninstall.sha1")
+
     if os.path.isfile(state_file_path):
         with open(state_file_path) as state_file:
-            version = int(state_file.read())
+            version = state_file.read()
         if version == expected_version:
+            print 'Python uninstalls unchanged, skipping...'
             return
 
     # Run pip to find the packages we need to get rid of.  Believe it or not,
@@ -177,27 +192,13 @@ def uninstall_python_packages():
     # to really really get rid of it.
     for _ in range(3):
         uninstalled = False
-        frozen = sh("pip freeze", capture=True).splitlines()
+        frozen = sh("pip freeze", capture=True)
 
-        # Uninstall South
-        if any(line.startswith("South") for line in frozen):
-            sh("pip uninstall --disable-pip-version-check -y South")
-            uninstalled = True
-
-        # Uninstall edx-val
-        if any("edxval" in line for line in frozen):
-            sh("pip uninstall --disable-pip-version-check -y edxval")
-            uninstalled = True
-
-        # Uninstall django-storages
-        if any("django-storages==" in line for line in frozen):
-            sh("pip uninstall --disable-pip-version-check -y django-storages")
-            uninstalled = True
-
-        # Uninstall django-oauth2-provider
-        if any(line.startswith("django-oauth2-provider==") for line in frozen):
-            sh("pip uninstall --disable-pip-version-check -y django-oauth2-provider")
-            uninstalled = True
+        for package_name in PACKAGES_TO_UNINSTALL:
+            if package_in_frozen(package_name, frozen):
+                # Uninstall the pacakge
+                sh("pip uninstall --disable-pip-version-check -y {}".format(package_name))
+                uninstalled = True
 
         if not uninstalled:
             break
@@ -208,7 +209,24 @@ def uninstall_python_packages():
 
     # Write our version.
     with open(state_file_path, "w") as state_file:
-        state_file.write(str(expected_version))
+        state_file.write(expected_version)
+
+
+def package_in_frozen(package_name, frozen_output):
+    """Is this package in the output of 'pip freeze'?"""
+    # Look for either:
+    #
+    #   PACKAGE-NAME==
+    #
+    # or:
+    #
+    #   blah_blah#egg=package_name-version
+    #
+    pattern = r"(?mi)^{pkg}==|#egg={pkg_under}-".format(
+        pkg=re.escape(package_name),
+        pkg_under=re.escape(package_name.replace("-", "_")),
+    )
+    return bool(re.search(pattern, frozen_output))
 
 
 @task