[Python-ideas] Replacing the if __name__ == "__main__" idiom (was Re: making a module callable)

[Nick Coghlan]

On 26 Nov 2013 05:51, "Guido van Rossum" <guido at python.org> wrote:
>
> On Mon, Nov 25, 2013 at 11:42 AM, Barry Warsaw <barry at python.org> wrote:
>>
>> On Nov 26, 2013, at 01:12 AM, Steven D'Aprano wrote:
>>
>> >(1) Keep the status quo.
>>
>> I'd have no problem with this.  The current idiom doesn't seem broken to
me,
>> nor is it that hard to type.  I also don't think it's very hard to
discover
>> given how common it is.
>
>
> All agreed, yet it is not that easy to type either (underscores and
quotes require the shift key). Perhaps more important, it causes everyone
who sees it first to wonder why the idiom isn't simpler.
>
>>
>> >if __main__:
>>
>> If we *had* to make this easier to type, this would be my choice.  It
doesn't
>> even have to be read-only, given that __name__ can be messed with, but
usually
>> isn't.  Why then worry about __main__ getting messed with?
>
>
> The problem with this is, how would you implement this? You can either
make __main__ a builtin object with a magic __bool__() method, or you can
plunk a bool named __main__ in every module namespace. I don't much like
either.

Shadowing would allow this to work without magic and with changes to only
two modules: you could have a builtin __main__ that was always False and
then set a __main__=True attribute in the main module.

This still teaches the lesson about runtime introspection *and* could be
used to teach an important lesson about name shadowing.

Like Barry, this is my favourite of the suggestions so far, but I'm still
not sure it's worth the hassle:

- any such code would automatically be 3.5+ only (failing with NameError on
earlier versions)
- anything that emulates __main__ execution in a namespace other than the
interpreter provided one would also need to be updated to set the new
attribute
- it adds "Why is __name__ wrong in __main__?" to the list of historical
relics that can only be explained in terms of "the modern alternative
didn't always exist"

Potentially still a net win, though - call it +0 from me.

Cheers,
Nick.

>
> --
> --Guido van Rossum (python.org/~guido)
>
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20131126/79ebeeac/attachment.html>