= Subclassing Dictionaries =

The process differs by Python version.

== Python-2.2 ==

Derive from {{{dict}}}.

ex:

{{{
#!python
class Msg(dict):

    __slots__ = [] # no attributes

    def __init__(self, msg_type, kv_dict = {}):
        dict.__init__(self)
        self["msg-type"] = msg_type
        self.update(kv_dict)

    def Type(self):
        return self["msg-type"]

    def __getitem__(self, k):
        return self.get(k, None)

    def __delitem__(self, k):
        if self.has_key(k):
            dict.__delitem__(self, k)

    def __str__(self):
        pp = pprint.pformat(dict(self))
        return "%s:  %s" % (self.Type(), pp)
}}}

The {{{__slots__}}} line indicates that Msg has no attributes of its own, preserving memory; see UsingSlots.

== See Also ==

[[Python-2.2]], SubclassingBuiltInTypes, UsingSlots

== Questions ==

  * Is this bad Python-2.2 code? Make improvements..! I ''do'' think it's worth showing how to use slots in the context of subclassing dict; In many cases, I think, people would want to do it. I ''do'' wonder if slots should be specified before or after the initializer- something to put on the UsingSlots page. -- LionKimbro <<DateTime(2003-09-07T17:07:24Z)>>
  [[lwickjr]]: Before, I think, collected with the other declaritives.