Sorry, forgot to use "reply to all"
---------- Forwarded message --------- From: André Roberge firstname.lastname@example.org Date: Sat, Nov 14, 2020 at 11:06 AM Subject: Re: [Python-ideas] Re: Global flag for whether a module is __main__ To: Steven D'Aprano email@example.com
On Sat, Nov 14, 2020 at 10:45 AM Steven D'Aprano firstname.lastname@example.org wrote:
On Sat, Nov 14, 2020 at 08:10:44AM -0400, André Roberge wrote:
What if you import the `__main__` module? What does `__imported__` say now, and how do you check for "running as a script" if `__main__` has imported itself -- or some other module has imported it?
Running a module (no matter what its name is) from a command line would
__imported__ to False for that module. Using import some_module (or __import__("some_module")) would set some_module.__imported__ to True.
Do you understand that a module can be both run and imported at the same time?
# example.py import __main__ print(__main__.__file__)
As others have mentioned, many beginners are thoroughly confused by the
meaning of the idiom
if __name__ == "__main__": ...
The idea behind the name __imported__ (and, I gather, somewhat similar to the original suggestion of __main__ that started this thread) is to reduce such confusion.
For what I had in mind, the semantic would be the same as though the following was inserted at the top of the module:
__imported__ = True if __name__ == "__main__": __imported__ = False
If you save that snippet as "example.py", and then run it:
you have an example of a module that is being run and imported simultaneously.
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The module __main__ is somewhat special. It's there from the very beginning (so far as I can tell). $ python3 -c 'import __main__; print(__main__)' <module '__main__' (built-in)>
And without importing __main__. $ python3 -c 'import sys; print(sys.modules["__main__"])' <module '__main__' (built-in)>
In light of this, it seems to me that the technical implementation of the proposal amounts to
1. When creating a new module object, set __main__ = False
2. When initializing the built-in __main__ module, set __main__ = True
I don't see a technical problem in the implementation of this idea. (I suspect the same rules will also work for C-coded modules.)
Whether a good idea or not is another question.
On Sat, Nov 14, 2020 at 05:22:41PM +0000, Jonathan Fine wrote:
The module __main__ is somewhat special. It's there from the very beginning (so far as I can tell).
- When initializing the built-in __main__ module, set __main__ = True
The `__main__` module is not so much a special built-in module as a role given to any old module. The `__main__` module is whatever module gets executed as the main module, if any, otherwise whatever module object gets created to house the top level scope of the Python interpreter.