If you ask me, I think that when the importing
system finds both a .py and a .pyc for a module,
then it should ignore all co_filename and replace
them with the real path of the .py file.  I can't
see any point of not doing so.

There are many other quirks caused by .pyc files
accidentally remaining around, but we cannot fix them
all as long as the .pyc files are at the same time
a cache for performance reason and a redistributable
program format (e.g. if "rm x.py" or "svn up" deletes
a .py file, then the module is still importable via
the .pyc left behind, a great way to oversee the fact
that imports elsewhere in the project need to be
updated).