Fix setuptools infinite loop bug triggered by python-saml

pavelib/prereqs.py

@@ -16,6 +16,7 @@ PYTHON_REQ_FILES = [
     'requirements/edx/github.txt',
     'requirements/edx/local.txt',
     'requirements/edx/base.txt',
+    'requirements/edx/post.txt',
 ]
 
 # Developers can have private requirements, for local copies of github repos,

requirements/edx/base.txt

@@ -44,7 +44,6 @@ glob2==0.3
 gunicorn==0.17.4
 httpretty==0.8.3
 lazy==1.1
-lxml==3.4.4
 mako==0.9.1
 Markdown==2.2.1
 --allow-external meliae
@@ -69,7 +68,6 @@ python-memcached==1.48
 python-openid==2.2.5
 python-dateutil==2.1
 python-social-auth==0.2.11
-python-saml==2.1.3
 pytz==2015.2
 pysrt==0.4.7
 PyYAML==3.10
@@ -90,6 +88,9 @@ unicodecsv==0.9.4
 django-require==1.0.6
 pyuca==1.1
 
+# This needs to be installed *after* Cython, which is in pre.txt
+lxml==3.4.4
+
 # Used for shopping cart's pdf invoice/receipt generation
 reportlab==3.1.44
 

requirements/edx/post.txt

+# DON'T JUST ADD NEW DEPENDENCIES!!!
+#
+# If you open a pull request that adds a new dependency, you should notify:
+#   * @mollydb - to check licensing
+#   * support@edx.org - to check system requirements
+
+# This needs to be installed *after* lxml, which is in base.txt.
+# python-saml pulls in lxml as a dependency, and due to a bug in setuptools,
+# trying to compile lxml as a dependency causes setuptools to go into an
+# infinite loop and run out of memory. Because why would you trust a
+# dependency management tool to manage dependencies for you?
+python-saml==2.1.3