On the python-ideas list, someone made a wild proposal to add descriptors to dictionaries.
None of the respondents seemed to realize that you could (not should, just could) already implement this using hooks already present in the language. I'm posting an example here because I thought you all might find it to be both interesting and educational. For more details on how it works and how it relates to descriptors, see http://mail.python.org/pipermail/python-ideas/2011-March/009657.html Raymond ---- sample code ---- class MyDict(object): def __init__(self, mapping): self.mapping = mapping def __getitem__(self, key): value = self.mapping[key] if hasattr(value, '__get__'): print('Invoking descriptor on', key) return value.__get__(key) print('Getting', key) return value def __setitem__(self, key, value): self.mapping[key] = value class Property: def __init__(self, getter): self.getter = getter def __get__(self, key): return self.getter(key) if __name__ == '__main__': md = MyDict({}) md['x'] = 10 md['_y'] = 20 md['y'] = Property(lambda key: md['_'+key]) print(eval('x+y+1', {}, md)) ---- output ---- Getting x Invoking descriptor on y Getting _y 31 -- http://mail.python.org/mailman/listinfo/python-list
