"Mac" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Under certain circumstances isinstance() seems to return incorrect
> value for me. I'm using Python 2.3 (latest from Debian's unstable).
> Here's a sample program... the multi-module nature of the code is key.
The key, which my debug addition below should help you see, is a
consequence of the mutually recursive definitions of the two modules, with
one of them also being the main module. This is a recipe for confusing
results that is best avoided. But I believe you could also get the same
confusing result with one file that imported itself directly rather than
indirectly via a second file.
> === test.py ===
>
> class Foo:
> pass
> def test():
> from test2 import make_me_a_foo
> foo = make_me_a_foo()
Try adding
print id(foo.__class__), foo.__class__
print id(Foo), Foo
> if isinstance(foo, Foo):
> print "is a Foo"
> else:
> print "is NOT a Foo!"
>
> if __name__ == "__main__":
> test()
> === test2.py ===
>
> from test import Foo
>
> def make_me_a_foo():
> return Foo()
> When I run "python test.py", I get "is NOT a Foo!", when the object
> clearly IS a Foo! Am I missing something
Yes, the ambiguity of Foo, which the print statements should reveal.
Deriving Foo from object to make it newstyle should give similar behavior.
> or is this a bug?
Pretty sure not. It is hard to go wrong comparing ids for equality.
Terry J. Reedy
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