[ python-Bugs-1317376 ] irregular behavior within class using __setitem__

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Bugs item #1317376, was opened at 2005-10-08 02:27
Message generated for change (Comment added) made by capnstabn
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Category: Python Interpreter Core
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: capnSTABN (capnstabn)
Assigned to: Nobody/Anonymous (nobody)
Summary: irregular behavior within class using __setitem__

Initial Comment:
i found two bugs vaguely similar to this posted but i 
think they were different bugs in theory, and both were 
deemed 'features' anyway so ... :p

basically the class is a modified list, being used as a 
queue

what happens is, when hotswapping the __setitem__ 
functionality, unless explicitly calling __setitem__, the 
old __setitem__ continues to be called

this is very odd and as far as i can tell the behavior is 
undocumented


class Queue(list):
def __setitem__(self, a, v):
print "old setitem"
def mysetitem(self, i, v):
print "new setitem"
def use_mysetitem(self):
self.__setitem__ = self.mysetitem

x = Queue()

x[1] = 2

x.__setitem__(2, 3)

x.use_mysetitem()
x[3] = 4

x.__setitem__(4, 5)


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>Comment By: capnSTABN (capnstabn)
Date: 2005-10-08 03:14

Message:
Logged In: YES 
user_id=1126596

err, yeh it does 8)
the last TWO prints should display new setitem


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Comment By: Nick Coghlan (ncoghlan)
Date: 2005-10-08 03:09

Message:
Logged In: YES 
user_id=1038590

This problem doesn't exist in Python 2.4:

Py> class Queue(list):
...   def __setitem__(self, a, v):
...     print "old setitem"
...   def mysetitem(self, i, v):
...     print "new setitem"
...   def use_mysetitem(self):
...     self.__setitem__ = self.mysetitem
...
Py> x = Queue()
Py>
Py> x[1] = 2
old setitem
Py>
Py> x.__setitem__(2, 3)
old setitem
Py>
Py> x.use_mysetitem()
Py> x[3] = 4
old setitem
Py>
Py> x.__setitem__(4, 5)
new setitem


----------------------------------------------------------------------

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