The inspect.getmodule function crashes if packages are installed that futz with sys.modules while they are being tested for module status or the like.  I'm not actually sure which packages are doing this, but the symptom is the for loop over sys.modules raises an Exception because it is modified while the loop is running.

This is *not* a problem in Python 2.x because sys.modules.items() returns a copy of the dictionary instead of an iterator, and 3.x changes that behavior.  The comment above the for loop makes it clear that the expected behavior is a copy rather than an iterator, so the attached patch corrects the problem by simply wrapping the items() call in list().

You are certainly right, but I wonder how this can happen.
Are there modules which import something just by looking at them?
Or is is some race condition due to another running thread?

Maybe it can be caused by an installation happening during the loop.  I agree with Erik’s reading of the comment and patch, and don’t think a test is needed.

The package that triggers it for me is the py (http://pypi.python.org/pypi/py) package - when in gets imported, it does some trick with sys.modules that is in place to get around some pickling restriction, but that means sys.modules is altered during the import of the `py` package... and that triggers the exception.

When a package is imported sys.modules changes... nothing special here.
But it's true true that py.std, for example, is a "lazy" module with a special __getattr__ that will import submodules.

Patch looks good to me as well.

New changeset 2ef359d7a2e9 by Éric Araujo in branch '3.2':
Fix inspect.getmodule to use a copy of sys.modules for iteration (#13487).
http://hg.python.org/cpython/rev/2ef359d7a2e9

Committed, thanks.