[Python-ideas] PEP for executing a module in a package containing relative imports
brett at python.org
Fri Apr 20 19:09:55 CEST 2007
On 4/19/07, Steven Bethard <steven.bethard at gmail.com> wrote:
> On 4/19/07, Brett Cannon <brett at python.org> wrote:
> > Let me know what you think. I especially want to hear which proposal
> > people prefer; the one in the PEP or the one in the Open Issues
> > section. Plus I wouldn't mind suggestions on a title for this PEP.
> As you've probably already guessed, I prefer the::
> if __main__:
> version. I don't think I've ever used sys.modules['__main__'].
Yeah, I figured you would. =)
> > Transition Plan
> > ===============
> > Using this solution will not work directly in Python 2.6. Code is
> > dependent upon the semantics of having ``__name__`` set to
> > ``'__main__'``. There is also the issue of pre-existing global
> > variables in a module named ``__main__``.
> Could you explain a bit why __main__ couldn't be inserted into modules
> before the module is actually executed? E.g. something like::
> >>> module_text = '''\
> ... __main__ = 'foo'
> ... print __main__
> ... '''
> >>> import new
> >>> mod = new.module('mod')
> >>> mod.__main__ = True
> >>> exec module_text in mod.__dict__
> >>> mod.__main__
> I would have thought that if Python inserted __main__ before any of
> the module contents got exec'd, it would be backwards compatible
> because any use of __main__ would just overwrite the default one.
That's right, and that is the problem. That would mean if __main__
was false but then overwritten by a function or something, it suddenly
became true. It isn't a problem in terms of whether the code will
run, but whether the expected semantics will occur.
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