[Tutor] Advantage of subclassing UserDict and UserList

[Kirby Urner]

Andrei Kulakov:


>Yes, you can for example make ordered dict:
>
>class SortedDict(UserDict.UserDict):
>     """Sorted dictionary for dict of directories"""
>     def keys(self):
>         l = self.data.keys()
>         l.sort()
>         return l
>     def items(self):
>         l = self.data.items()
>         l.sort()
>         return l

Note that in 2.2 you can subclass list and dictionary
directly (though I think in 2.2b2 it's dict).  E.g.

    class SortedDict(dictionary):
         _keys = dictionary.keys
         _items = dictionary.items

         def keys(self):
            L = self._keys()
            L.sort()
            return L
         def items(self):
            L = self._items()
            L.sort()
            return L

  >>> b = SortedDict({'D':9,'C':2,'A':1, 'E':5,})
  >>> b._items()
  [('A', 1), ('C', 2), ('E', 5), ('D', 9)]
  >>> b.items()
  [('A', 1), ('C', 2), ('D', 9), ('E', 5)]
  >>> b._keys()
  ['A', 'C', 'E', 'D']
  >>> b.keys()
  ['A', 'C', 'D', 'E']

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