instance attributes not inherited?

[John M. Gabriele]

The following short program fails:


----------------------- code ------------------------
#!/usr/bin/python

class Parent( object ):
     def __init__( self ):
         self.x = 9
         print "Inside Parent.__init__()"


class Child( Parent ):
     def __init__( self ):
         print "Inside Child.__init__()"


p1 = Parent()
p2 = Parent()
c1 = Child()
foo = [p1,p2,c1]

for i in foo:
     print "x =", i.x
----------------- /code ----------------------



yielding the following output:

---------------- output ------------------
Inside Parent.__init__()
Inside Parent.__init__()
Inside Child.__init__()
x = 9
x = 9
x =
Traceback (most recent call last):
   File "./foo.py", line 21, in ?
     print "x =", i.x
AttributeError: 'Child' object has no attribute 'x'
---------------- /output ---------------------


Why isn't the instance attribute x getting inherited?

My experience with OOP has been with C++ and (more
recently) Java. If I create an instance of a Child object,
I expect it to *be* a Parent object (just as, if I subclass
a Car class to create a VW class, I expect all VW's to *be*
Cars).

That is to say, if there's something a Parent can do, shouldn't
the Child be able to do it too? Consider a similar program:

------------------- code ------------------------
#!/usr/bin/python


class Parent( object ):
     def __init__( self ):
         self.x = 9
         print "Inside Parent.__init__()"

     def wash_dishes( self ):
         print "Just washed", self.x, "dishes."


class Child( Parent ):
     def __init__( self ):
         print "Inside Child.__init__()"


p1 = Parent()
p2 = Parent()
c1 = Child()
foo = [p1,p2,c1]

for i in foo:
     i.wash_dishes()
------------------- /code -----------------------

But that fails with:

------------------- output ----------------------
Inside Parent.__init__()
Inside Parent.__init__()
Inside Child.__init__()
Just washed 9 dishes.
Just washed 9 dishes.
Just washed
Traceback (most recent call last):
   File "./foo.py", line 24, in ?
     i.wash_dishes()
   File "./foo.py", line 10, in wash_dishes
     print "Just washed", self.x, "dishes."
AttributeError: 'Child' object has no attribute 'x'
------------------- /output ---------------------

Why isn't this inherited method call working right?
Is this a problem with Python's notion of how OO works?

Thanks,
---J

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