I see this was reported as a debian bug. http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=665776 We encountered it as well. To reproduce, using virtualenv 1.7+ on Python 2.7.2 on Ubuntu, create a virtualenv. Move that virtualenv to a host with Python 2.7.3RC2 yields: jaraco@vdm-dev:~$ /usr/bin/python2.7 -V Python 2.7.3rc2 jaraco@vdm-dev:~$ env/bin/python -V Python 2.7.2 jaraco@vdm-dev:~$ env/bin/python -c "import os; os.urandom()" Traceback (most recent call last): File "<string>", line 1, in <module> AttributeError: 'module' object has no attribute 'urandom' This bug causes Django to not start properly (under some circumstances). I reviewed the changes between v2.7.2 and 2.7 (tip) and it seems there was substantial refactoring of the os and posix modules for urandom. I still don't fully understand why the urandom method is missing (because the env includes the python 2.7.2 executable and stdlib). I suspect this change is going to cause some significant backward compatibility issues. Is there a recommended workaround? Should I file a bug? Regards, Jason