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

[Chris Angelico]

On Tue, Nov 26, 2013 at 9:12 AM, Ron Adam <ron3200 at gmail.com> wrote:
> I was thinking that __main__ would be set to "__main__" first, then when the
> main module is loaded, it's __name__ attribute set to __main__ rather than
> "__main__".  Exactly as the first example above.

I thought you were describing assigning a particular string to
__name__, which is where the problem would come from. If it's being
set to "whatever's in __main__", then yes, your description is correct
and it's safe.

OTOH, what you now have is:

# standard idiom, everyone knows this works
if __name__ is __main__:

# use of actual thing: it's a string
print(__name__)

# everywhere else, this is the wrong thing to do:
if input() is "yes": do_dangerous_stuff()

So now you have to explain why it's right to use 'is', but only with
these things, which are magical. Possibly the easiest would be to
guarantee that __main__ and __name__ are sys.intern()'d, which could
then lead into an explanation of interning rather than an explanation
of magic.

ChrisA