[ python-Bugs-973579 ] Doc error on super(cls,self)

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Bugs item #973579, was opened at 2004-06-15 18:43
Message generated for change (Comment added) made by jimjjewett
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Category: Documentation
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: David MacQuigg (macquigg)
Assigned to: Nobody/Anonymous (nobody)
Summary: Doc error on super(cls,self)

Initial Comment:
In both the Library Reference, section 2.1, and in the 
Python 2.2 Quick Reference, page 19, the explanation 
for this function is:

super( type[, object-or-type]) 
   Returns the superclass of type. ...

This is misleading.  I could not get this function to work 
right until I realized that it is searching the entire MRO, 
not just the superclasses of 'type'.  See 
comp.lang.python 6/11/04, same subject as above, for 
further discussion and an example.

I think a better explanation would be:

super(cls,self).m(arg)

   Calls method 'm' from a class in the MRO (Method 
Resolution Order) of 'self'.  The selected class is the first 
one which is above 'cls' in the MRO and which 
contains 'm'.

The 'super' built-in function actually returns not a class, 
but a 'super' object.  This object can be saved, like a 
bound method, and later used to do a new search of the 
MRO for a different method to be applied to the saved 
instance.


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Comment By: Jim Jewett (jimjjewett)
Date: 2004-06-21 10:50

Message:
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user_id=764593

Would an expanded example also help?  

I'm not sure I like my own wording yet, but ... I propose it as a 
straw man.

"""super returns the next parent class[1]

class A(object): pass

class B(A):
    def meth(self, arg):
        super(B, self).meth(arg)

class C(A): pass

class D(B, C): pass

d=D()
d.meth()

In this case, the super(B, self) call will actually return a 
reference to class C.  Class C is not a parent of class B, but it 
is the next parent for this particular instance d of class B.


[1] Actually, a super class mimicing the parent class.  

"""

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