[Python-Dev] Virtualenv not portable from Python 2.7.2 to 2.7.3 (os.urandom missing)

[Carl Meyer]

Hi Jason,

On 03/28/2012 12:22 PM, Jason R. Coombs wrote:
> 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 at vdm-dev:~$ /usr/bin/python2.7 -V
> 
> Python 2.7.3rc2
> 
> jaraco at vdm-dev:~$ env/bin/python -V
> 
> Python 2.7.2
> 
> jaraco at 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).

In Python 2.6.8/2.7.3, urandom is built into the executable. A
virtualenv doesn't contain the whole stdlib, only the bits necessary to
bootstrap site.py. So the problem arises from trying to use the 2.7.3
stdlib with a 2.7.2 interpreter.

> I suspect this change is going to cause some significant backward
> compatibility issues. Is there a recommended workaround? Should I file a
> bug?

The workaround is easy: just re-run virtualenv on that path with the new
interpreter.

I was made aware of this issue a few weeks ago, and added a warning to
the virtualenv "news" page:
http://www.virtualenv.org/en/latest/news.html  I'm not sure where else
to publicize it.

Carl

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