Inheriting from OrderedDict causes problem

Bruce Eckel lists.eckel at gmail.com
Wed Feb 22 17:53:52 CET 2012


Notice that both classes are identical, except that one inherits from
dict (and works) and the other inherits from OrderedDict and fails.
Has anyone seen this before? Thanks.

import collections

class Y(dict):
    def __init__(self, stuff):
        for k, v in stuff:
            self[k] = v

# This works:
print Y([('a', 'b'), ('c', 'd')])

class X(collections.OrderedDict):
    def __init__(self, stuff):
        for k, v in stuff:
            self[k] = v

# This doesn't:
print X([('a', 'b'), ('c', 'd')])

""" Output:
{'a': 'b', 'c': 'd'}
Traceback (most recent call last):
  File "OrderedDictInheritance.py", line 17, in <module>
    print X([('a', 'b'), ('c', 'd')])
  File "OrderedDictInheritance.py", line 14, in __init__
    self[k] = v
  File "C:\Python27\lib\collections.py", line 58, in __setitem__
    root = self.__root
AttributeError: 'X' object has no attribute '_OrderedDict__root'
"""



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