Python returns a different exit status when an exception is raised and -m is used as opposed to just running a module.

A short example, let's call it foo.py:

    def main():
        raise ValueError()

    if __name__ == '__main__':
        main()

When run with python foo.py the exit status of the process is 1. If run with python -mfoo the exit status of the process is 255.

Technically, it returns -1 (which later gets coerced to an unsigned value).

However, there's no good reason for the inconsistency - the offending line (663) in main.c should be changed to be:

    sts = (RunModule(module, 1) != 0);

It is currently just:

    sts = RunModule(module, 1);

An additional test in test_cmd_line_script is also needed to ensure that both variants give a returncode of 1 in the future.

Fixed for 3.3. Does this need to be back ported as well?

And by 'Fixed' I of course meant 'Patched, awaiting review'.

New changeset fcbd3bda7c0f by Senthil Kumaran in branch '3.2':
Fix issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/fcbd3bda7c0f

New changeset 1186d68715cc by Senthil Kumaran in branch 'default':
Fix issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/1186d68715cc

New changeset 55b3de6d701e by Senthil Kumaran in branch '2.7':
Fix closes issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/55b3de6d701e

Thanks for the patch Jeff and thanks for the guidance, Nick. 
Committed this in all branches.