[Python-ideas] Module aliases and/or "real names"

Nick Coghlan ncoghlan at gmail.com
Wed Jan 5 02:55:04 CET 2011

On Wed, Jan 5, 2011 at 8:52 AM, Guido van Rossum <guido at python.org> wrote:
> Hmm... I starred this and am finally dug out enough to comment.
> Would it be sufficient if the __module__ attribute of classes and
> functions got set to the "canonical" name rather than the "physical"
> name?
> You can currently get a crude version of this by simply assigning to
> __name__ at the top of the module.
> That sounds like it would be too confusing, however, so perhaps we
> could make it so that, when the __module__ attribute is initialized,
> it first looks for __canonical__ and then for __name__?
> This may still be too crude though -- I looked at the one example I
> could think of where this might be useful, the unittest package, and
> realized that it would set __module__ to 'unittest' even for classes
> that are not actually re-exported via the unittest namespace.
> So maybe it would be better in that case to just patch the __module__
> attribute of all the public classes in unittest/__import__.py?

I did think about that - for classes, it would probably be sufficient,
but for functions the fact that we'd be breaking the identity that
"f.__globals__ is sys.modules[f.__module__]" scares me. Then again,
the fact that "f.__module__ != f.__globals__['__name__']" would
provide exactly the indicator of "two names" that I am talking about
(at least where functions are concerned) - things like pydoc and the
inspect module could definitely be updated to check both module names.
On the gripping hand, there would still be problems with things like
methods and nested classes and functions (unless tools were provided
to recurse down through a class to update the subcomponents as well as
the class itself).

So perhaps the granularity on my initial suggestion wasn't fine enough
- if the "__canonical__" idea was extended to all objects with a
__module__ attribute, then objects could either be relocated at
creation time (by setting __canonical__ in the module globals), or
after the fact by assigning to the __canonical__ attribute on the

> OTOH for things named __main__, setting __canonical__ (automatically,
> by -m or whatever other mechanism starts execution, like "python
> <filename>" might actually work.

Yes, although a related modification is needed in those cases (to
actual insert the module being executed into sys.modules under its
module name as well as under __main__).

> On the third hand, maybe you've finally hit upon a reason why the "if
> __name__ == '__main__': main()" idiom is bad...

I can't take credit for that particular observation - I've certainly
heard others complain about that in the context of pickling objects
over the years. It is one of the main things that got me thinking
along these lines in the first place.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

More information about the Python-ideas mailing list