objects as mutable dictionary keys

[Andrew Dalke]

Andrew Koenig:
> If d is a dict and t1 and t2 are tuples, and t1 == t2, then d[t1] and d[t2] 
> are the same element.

So long as the elements of t1 and t2 are well-behaved.

>>> class Spam:
...   def __hash__(self):
...     return id(self)
...   def __eq__(self, other):
...     return True
... 
>>> t1 = (Spam(),)
>>> t2 = (Spam(),)
>>> t1 == t2
True
>>> hash(t1) == hash(t2)
False
>>> d = {t1: "T1", t2: "T2"}
>>> d[t1] 
'T1'
>>> d[t2] 
'T2'
>>> d[t1] == d[t2] 
False
>>> d[t1] is d[t2] 
False
>>> 

Dictionaries have the extra requirement that if
k1 == k2 then hash(k1) == hash(k2).


				Andrew
				dalke at dalkescientific.com