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

[Rob Cliffe]

On 25/11/2013 14:12, Steven D'Aprano wrote:

> (4) Like #3 above, but make it a (read-only?) global variable, like
>      __debug__. Possibly spelled "__main__". The idiom becomes:
>
>
> if is_main:
>      ...
>
>
> if __main__:
>      ...
>
>
> Pros:
>
> - Some people might feel that "this is the main module" feels
>    more like a global variable than a function call.
>
> Cons:
>
> - If read-only, that requires some magic behind the scenes.
>
> - If not read-only, then people will mess about with it and
>    get confused.
>
> +0.5 if read-only, -0.5 if not.
>
I like this idea (a global variable called __main__), provided that it 
can be implemented without slowing down access to other variables.
Say __main__ did not exist as a real variable, so attempting to read it 
triggered a NameError behind the scenes.
The error handling code could then check for a name of '__main__' as a 
special case.  Does this make sense?

Con:
A variable which changes its value without being assigned to is more 
magical/unexpected than a function
(is_main()) which returns different values at different times.
But I think people would soon get used to it, and find it convenient.

The behaviour could be overridden (if the run-time allowed it) by 
defining a "real" variable called __main__.
Well, among consenting adults, why not?  It might even be useful.

Rob Cliffe