django.utils.module_loading.module_has_submodule yields false positives
The way I found this is a bit crazy, so I'm not going to describe it all, but the 2 important things are:
- I have some explicit relative imports.
- I wanted to make a template library named the same as the application it contains.
This generally should work (tried on a fresh project), but failed with a weird error in my project: "'currencies' is not a valid tag library: ImportError raised loading company.templatetags.currencies: No module named currencies". Of course there is no such module, because it's on "currencies.templatags" application.
So after some debuging it turned out that module_has_submodule returns a false positive. This is because it checks if name in sys.modules . To be honest, I didn't know about this, but it seems that Python sometimes also stores import misses by puting a None in to that dictionary. See this python-dev thread.
I reported this in 15114 which was a duplicate. But you may want to include the regression test I wrote.
http://code.djangoproject.com/attachment/ticket/15114/sys-modules-none.diff