[Python-Dev] PEP 395: Module Aliasing

[Ron Adam]

On 03/05/2011 06:33 PM, Nick Coghlan wrote:
> On Sun, Mar 6, 2011 at 4:11 AM, Ron Adam<rrr at ronadam.com>  wrote:
>> Adding a second references to the '__main__' module begins to blur the
>> purpose of sys.modules from being a place to keep imported modules to a
>> place that also has some ordering information.  (Practicality over purity?,
>> Or an indication of what direction to go in?)
>>
>> And, if you ask for keys, items, or values, you will need to filter out
>> '__main__' to avoid the double reference.
>>
>> So I was thinking, what if we make sys.modules a little smarter.  The
>> negative of that is, it would no longer be a simple dictionary object.
>>
>> First idea ...
>>
>> Add a __main__ attribute to sys.modules to hold the name of the main module.
>>
>> Override modules.__setitem__, so it will catch '__main__' and set
>> modules.__main__ to the name of the module, and put the module in under its
>> real name instead of '__main__'.
>>
>> Override modules.__getitem__, so it will catch '__main__' and return
>> self[self.__main__].
>>
>> Then keys(), values(), and items(), will not have the doubled main module
>> references in them.
>>
>> The name of the main module is easy to get.  ie... sys.modules.__main__
>>
>> sys.modules[__name__] will still return the correct module if __name__ ==
>> "__main__".
>
> That's quite an interesting idea - I hadn't even considered the
> implications of double counting the affected module when iterating
> over sys.modules in some fashion. That said, dropping `__main__` from
> the iteration might confuse existing code, so it may be better to have
> the lookup go the other way (i.e. define __missing__ on the dict
> subclass and return sys.modules['__main__'] if the key matches
> sys.modules.__main__).

     ... if the key matches sys.modules.__missing__

Works for me. ;-)

We can find a better name than __missing__ later.  (minor detail)

Cheers,
    Ron