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

[Jason R. Coombs]

> -----Original Message-----
> From: python-dev-bounces+jaraco=jaraco.com at python.org [mailto:python-
> dev-bounces+jaraco=jaraco.com at python.org] On Behalf Of Carl Meyer
> Sent: Wednesday, 28 March, 2012 14:48
> 
> The workaround is easy: just re-run virtualenv on that path with the new
> interpreter.
> 

Thanks for the quick response Carl. I appreciate all the work that's been
done.

I'm not sure the workaround is as simple as you say. Virtualenv doesn't
replace the 'python' exe if it already exists (because it may already exist
for a different minor version of Python (3.2, 2.6)). So the procedure is
probably something like this:

For each <minor> version of Python the virtualenv wraps (ls
env/bin/python?.?):
1) Run env/bin/python -V. If the result starts with "Python <minor>", remove
env/bin/python.
2) Determine if that Python version uses distribute or setuptools.
3) Run virtualenv --python=python<minor> env (with --distribute if
appropriate)

I haven't yet tested this procedure, but I believe it's closer to what will
need to be done. There are probably other factors. Unfortunately, to
reliably repair the virtualenv is very difficult, so we will probably opt
with re-deploying all of our virtualenvs.

Will the release notes include something about this change, since it will
likely have broad backward incompatibility for all existing virtualenvs? I
wouldn't expect someone in operations to read the virtualenv news to find
out what things a Python upgrade will break. Indeed, this update will
probably be pushed out as part of standard, unattended system updates.

I realize that the relationship between stdlib.os and posixmodule isn't a
guaranteed interface, and the fact that it breaks with virtualenv is a
weakness of virtualenv. Nevertheless, virtualenv has become the defacto
technique for Python environments. Putting my sysops cap on, I might
perceive this change as being unannounced (w.r.t. Python) and having
significant impact on operations. I would think this impact deserves at
least a note in the release notes.

Regards,
Jason
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