[Python-Dev] avoiding accidental shadowing of top-level libraries by the main module

Michael Foord fuzzyman at voidspace.org.uk
Tue Jul 13 12:45:20 CEST 2010


On 13/07/2010 01:30, Steven D'Aprano wrote:
> On Tue, 13 Jul 2010 08:05:24 am Nick Coghlan wrote:
>    
>> On Tue, Jul 13, 2010 at 7:47 AM, Fred Drake<fdrake at acm.org>  wrote:
>>      
>>> On Mon, Jul 12, 2010 at 5:42 PM, Michael Foord
>>>
>>> <fuzzyman at voidspace.org.uk>  wrote:
>>>        
>>>> I'm sure Brett will love this idea, but if it was impossible to
>>>> reimport the script being executed as __main__ with a different
>>>> name it would solve these problems.
>>>>          
>>> Indeed!  And I'd be quite content with such a solution, since I
>>> consider scripts and modules to be distinct.
>>>        
>> And here I've been busily blurring that distinction for years ;)
>>
>> (actually, the whole "name == '__main__'" idiom meant the distinction
>> was already pretty blurry long before I got involved)
>>      
> I would hate it if that distinction was un-blurred. Most of my modules
> include a section "if __name__ == '__main__': run_tests(), and some of
> them do significantly more than that. A few of them import themselves
> so they can pass the module object to another module.
>
>
>    

Reimporting yourself (and creating a second version of the module with 
new versions of all the classes / constants / functions / etc) doesn't 
seem like a good way of doing that though. If you need the module object 
you can always do:

module = sys.modules[__name__]

Michael Foord

>> I take it the concrete proposal here is if the filename of a new
>> module matches either __main__.__file__ or __main__.__cached__, then
>> that module should be ignored completely for import purposes allowing
>> a module with the same name later on sys.path to be found?
>>
>> I'm not sure I like that, I'd be more inclined to just return the
>> __main__ module in that case rather than letting the search continue
>> further down sys.path (although I agree the current semantics of
>> getting two copies of the same module under different names in this
>> case are less than ideal).
>>      
> Yes, that's a weird corner case. I don't see any advantage to keeping
> that behaviour.
>
>
>
>    


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