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I am building a class which subclasses dict , and overrides __setitem__ . I would like to be certain that my method will be called in all instances where dictionary items could possibly be set. I have discovered three situations where Python (in this case, 2.6.4) does not call my overridden __setitem__ method when setting values, and instead calls PyDict_SetItem directly In the constructor In the setdefault method In the update method As a very simple test: class MyDict(dict): def __setitem__(self, key, value): print "Here" super(MyDict, self).__setitem__(key, str(value).upper()) >>> a = MyDict(abc=123) >>> a['def'] = 234 Here >>> a.update({'ghi': 345}) >>> a.setdefault('jkl', 456) 456 >>> print a {'jkl': 456, 'abc': 123, 'ghi': 345, 'def': '234'} You can see that the overridden method is only called when setting the items explicitly. To get Python to always call my __setitem__ method, I have had to reimplement those three methods, like this: class MyUpdateDict(dict): def __init__(self, *args, **kwargs): self.update(*args, **kwargs) def __setitem__(self, key, value): print "Here" super(MyUpdateDict, self).__setitem__(key, value) def update(self, *args, **kwargs): if args: if len(args) > 1: raise TypeError("update expected at most 1 arguments, got %d" % len(args)) other = dict(args[0]) for key in other: self[key] = other[key] for key in kwargs: self[key] = kwargs[key] def setdefault(self, key, value=None): if key not in self: self[key] = value return self[key] Are there any other methods which I need to override, in order to

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