No need to update __getitem__, since the modified __setitem__ drops in
the reverse values. But __delitem__ needs overriding, and some special
guard needs to be added to __setitem__ to prevent orphaning any old
value:key entries.
-- Paul
Here's one possible solution:
class SymmetricDict(dict):
def __delitem__(self,x):
v = self[x]
super(SymmetricDict,self).__delitem__(x)
super(SymmetricDict,self).__delitem__(v)
def __setitem__(self,k,v):
if k in self:
del self[k]
if v in self:
del self[v]
super(SymmetricDict,self).__setitem__(k,v)
super(SymmetricDict,self).__setitem__(v,k)
sd = SymmetricDict()
sd["A"] = 1
print sd["A"]
print sd[1]
sd["A"] = 2
print sd["A"]
print sd[2]
print sd[1]
prints:
1
A
2
A
Traceback (most recent call last):
File "symmetricDict.py", line 25, in ?
print sd[1]
KeyError: 1
--
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