[ python-Bugs-965562 ] isinstance fails to recognize instance

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Bugs item #965562, was opened at 2004-06-03 09:55
Message generated for change (Comment added) made by ijorgensen
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Category: Python Interpreter Core
Group: Python 2.2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Ib Jørgensen (ijorgensen)
Assigned to: Nobody/Anonymous (nobody)
Summary: isinstance fails to recognize instance

Initial Comment:
I searched the bugbase and found a somewhat similar 
problem that was termed invalid (id 563730 )
I did however spend some time figuring out what was 
going wrong so..?

The following two modules document the problem:
MODULE A:
import b

class A:
    def __init__(self):
        self.name = "a"


if __name__ == "__main__":
    x = A()
    print "main",isinstance(x,A)
    y = b.B()
    y.notify(x)

MODULE B:
import a
class B:
    def __init__(self):
        self.name = "b"

    def notify(self,cl):
        print "notify",isinstance(cl,a.A)



if __name__ == "__main__":
    x = a.A()
    print isinstance(x,a.A)
    y = B()
    y.notify(x)

running module A gives inconsistent results
the printout is:
main True
notify False

The modules do have circular imports and it is clear that 
this is behind the problem - but that may happen in real 
life.


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>Comment By: Ib Jørgensen (ijorgensen)
Date: 2004-06-03 13:23

Message:
Logged In: YES 
user_id=1055299

I have no problems if you close this bug. I do however feel 
that it is quite subtle to distinguish classes by the rather 
random import order.


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Comment By: Walter Dörwald (doerwalter)
Date: 2004-06-03 12:43

Message:
Logged In: YES 
user_id=89016

The problem is not the circular import per se, but the fact 
that module a gets imported twice, once as the __main__ 
module (with it's version of the class A) and once as the 
module A (with it's own version of the class A).

>From Python's point of view these are two completely 
unrelated classes with on inheritance relationship whatsoever.

Can this bug be closed?

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