Op 2004-12-16, Fredrik Lundh schreef <[EMAIL PROTECTED]>: > Antoon Pardon wrote: > >>> how does the dictionary know if you want key value equality or key >>> identity equality? >> >> By the __hash__ and __eq__ methods you provide on your object. > > so what you're saying is that Python dictionaries should work just like > Python dictionaries work today. > > sorry for wasting my time.
In the end yes. I was a bit confused at first because others were asserting that python didn't allow mutable keys and gave reasons for why they thought that was a good thing. I didn't know better so originally just tried to argue why that would be a bad thing. As it turns out those assertions were wrong. Although the documentation on the python site does state this: http://docs.python.org/lib/typesmapping.html Only values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys. And the following: http://docs.python.org/ref/customization.html If a class defines mutable objects and implements a __cmp__() or __eq__() method, it should not implement __hash__(), since the dictionary implementation requires that a key's hash value is immutable (if the object's hash value changes, it will be in the wrong hash bucket). I find the latter to be misleading. The dictionary class probably doesn't require that a key's hash value is immutable, just that a key's hash value doesn't mutate during its lifecycle in the dictionary. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
