[Python-ideas] PEP for executing a module in a package containing relative imports

Brett Cannon brett at python.org
Sun Apr 22 20:44:56 CEST 2007

On 4/22/07, Christian Heimes <lists at cheimes.de> wrote:
> Steven Bethard wrote:
> > I think this PEP now needs to explicitly state that keeping the "am I
> > the main module?" idiom as simple as possible is *not* a goal. Because
> > everything I've seen (except for the original proposals in the PEP)
> > are substantially more complicated than the current::
> >
> >     if __name__ == '__main__':
> >
> I'm proposing the following changes:
> * sys.main is added which contains the dotted name of the main script.
>    This allows code like:
>      if __name__ == sys.main:
>          ...
>      main_module = sys.modules[sys.main]
> * __name__ is never mangled and contains always the dotted name of
>    the current module. It's not set to '__main__' any more.

That can't be true.  If I am in the directory /spam but I execute the
file /bacon/code.py, what is the name of /bacon/code.py supposed to
be?  It makes absolutely no sense unless sys.path happens to have
either / or /bacon.  This is why I wondered out loud if setting
whatever attribute that is chosen not to __main__ should only be done
with '-m' as that keeps it simple and clear instead of having to try
to reverse-engineer a file's __name__ attribute.

>You can
>    get the current module object with
>      this_module = sys.modules[__name__]
> * I'm against sys.modules['__main__] = main_module because it may
>    cause ugly side effects with reload.

I assume that key is a string?  There is a single quote that is not closed off.

> The same functionality is
>    available with sys.modules[sys.main]. The Zen Of Python says that
>    there should be one and only one obvious way.
>  > I guess I don't understand why we wouldn't be willing to put up with a
>  > new module attribute or builtin to minimize the boilerplate in pretty
>  > much every Python application out there.
> Why bother with the second price when you can win the first prize? In my
> opinion a __main__() function makes live easier than a __main__ module
> level variable. It's also my opinion that the main code should be in a
> function and not in the body of the module. I consider it good style
> because the code is unit testable (is this a word? *g*) and callable
> from another module while code in the body is not accessable from unit
> tests and other scripts.

People can stop wishing for this.  I am not going to be writing a PEP
supporting this.  I don't like it; never have.  I like how Python
handles things currently in terms of relying on how module are
executed linearly.

I am totally fine if people propose a competing PEP or try to
resurrect PEP 299, but I am not going to be the person who does that
leg work.


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