Re: Messing up with classes and their namespace

[Scott David Daniels]

Jean-Michel Pichavant wrote:

Hello world,

I had recently a very nasty bug in my python application. The context is quite complex, but in the end the problem can be resume as follow:

2 files in the same directory :

lib.py:
 >import foo
 >foo.Foo.BOOM='lib'

foo.py:
 >class Foo:
 >    BOOM = 'Foooo'
 >
 >if __name__=='__main__':
 >    import lib # I'm expecting BOOM to be set to 'lib'
 >    print Foo.BOOM

I was expecting 'lib' as output, but I got 'Fooo'. I don't really understand what python mechanism I'm messing with but I have the feeling I've misunderstood a very basic concept about class, namespace or whatever import notion.

I guess there is 2 different objects for the same class Foo. How I do I make both Foo objects the same object ?

OK, here is one solution (from which you may infer the problem):

lib.py:
    import __main__
    __main__.Foo.BOOM = 'lib'

foo.py:
    class Foo:
        BOOM = 'Foooo'

    if __name__ == '__main__':
        import lib # I'm expecting BOOM to be set to 'lib'
        print(Foo.BOOM)

Here is another solution:

lib.py:
    import foo
    foo.Foo.BOOM = 'lib'

foo.py:
    class Foo:
        BOOM = 'Foooo'

    if __name__ == '__main__':
        import sys
        sys.modules['foo'] = sys.modules['__main__']
        import lib # I'm expecting BOOM to be set to 'lib'
        print(Foo.BOOM)

Here is a demo of what is actually going wrong:

foo.py:
    class Foo:
        inside = __name__

    import foo

    if __name__ == '__main__':
        print(Foo is foo.Foo)
        print(Foo.inside, foo.Foo.inside)

And here is a fix
foo.py:
    if __name__ == '__main__':
        import sys
        sys.modules['foo'] = sys.modules['__main__']

    class Foo:
        inside = __name__

    import foo

    if __name__ == '__main__':
        print(Foo is foo.Foo)
        print(Foo.inside, foo.Foo.inside)


--Scott David Daniels
scott.dani...@acm.org
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