We hit some very weird behaviour recently while setting up a package
hierarchy. Robin Becker managed to distil this into a simple example.
Can anyone shed any light on what is happening below? Is Python
behaving as it should?
Create a package A, empty __init__.py, with modules as follows:
--------parent.py----------
class Parent:
pass
--------child.py------------
from parent import Parent
class Child(Parent):
pass
---------test.py--------
from parent import *
class Examiner:
def examine(self, arg):
print 'examining argument:'
print 'class of arg =3D', arg.__class__
print 'bases of arg =3D', arg.__class__.__bases__
print 'arg =3D', arg
if isinstance(arg, Parent):
print "arg is an instance of Parent"
else:
print "arg IS NOT an instance of Parent"
print
=20
if __name__=3D=3D'__main__':
from traceback import print_exc
import sys
def run0():
from A.child import Child
e =3D Examiner()
e.examine(Child())
def run1():
from A.child import Child
from A.test import Examiner
e =3D Examiner()
e.examine(Child())
run0()
run1()
Running this script produces the following output:
C:\users\andy\A>test.py
examining argument:
class of arg =3D A.child.Child
bases of arg =3D (<class A.parent.Parent at 7f9150>,)
arg =3D <A.child.Child instance at 7f9410>
arg IS NOT an instance of Parent
examining argument:
class of arg =3D A.child.Child
bases of arg =3D (<class A.parent.Parent at 7f9150>,)
arg =3D <A.child.Child instance at 7f83c0>
arg is an instance of Parent
Many thanks,
Andy Robinson
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