[Python-ideas] breaking out of module execution

[Georg Brandl]

On 24.04.2012 22:20, M.-A. Lemburg wrote:

>>> Think of code like this (let's assume the "break" statement is used
>>> for stopping module execution):
>>>
>>> """
>>> #
>>> # MyModule
>>> #
>>>
>>> ### Try using the fast variant
>>>
>>> try:
>>>     from MyModule_C_Extension import *
>>> except ImportError:
>>>     pass
>>> else:
>>>     # Stop execution of the module code object right here
>>>     break
>>>
>>> ### Ah, well, so go ahead with the slow version
>>>
>>> import os, sys
>>> from MyOtherPackage import foo, bar, baz
>>>
>>> class MyClass:
>>>     ...
>>>
>>> def MyFunc(a,b,c):
>>>     ...
>>>
>>> def main():
>>>     ...
>>>
>>> if __name__ == '__main__':
>>>     main()
>>> """
>> 
>> There's a subtle bug here that shows that the proposed feature has its
>> awkward points:  you probably want to execute the "if __name__ == '__main__'"
>> block in the C extension case as well.
> 
> No, you don't :-) If you would have wanted that to happen, you'd
> put the "if __name__..." into the else: branch.

Not sure I understand.  Your example code is flawed because it doesn't execute
the main() for the C extension case.  Of course you can duplicate the code in
the else branch, but you didn't do it in the first place, which was the bug.

Georg