Retrieving an object from a set
Ethan Furman
ethan at stoneleaf.us
Sat Jan 26 00:38:16 CET 2013
On 01/25/2013 03:14 PM, Arnaud Delobelle wrote:
> I've got a seemingly simple problem, but for which I cannot find a
> simple solution.
>
> I have a set of objects (say S) containing an object which is equal to
> a given object (say x). So
>
> x in S
>
> is true. So there is an object y in S which is equal to x. My
> problem is how to retrieve y, without going through the whole set.
> Here is a simple illustration with tuples (my actual scenario is not
> with tuples but with a custom class):
>
>>>> y = (1, 2, 3) # This is the 'hidden object'
>>>> S = set([y] + range(10000))
>>>> x = (1, 2, 3)
>>>> x in S
> True
>>>> x is y
> False
>
> I haven't found y. It's a very simple problem, and this is the
> simplest solution I can think of:
>
> class FindEqual(object):
> def __init__(self, obj):
> self.obj = obj
> def __hash__(self):
> return hash(self.obj)
> def __eq__(self, other):
> equal = self.obj == other
> if equal:
> self.lastequal = other
> return equal
>
>>>> yfinder = FindEqual(x)
>>>> yfinder in S
> True
>>>> yfinder.lastequal is y
> True
>
> I've found y! I'm not happy with this as it really is a trick. Is
> there a cleaner solution?
I don't know if there is a cleaner solution, and I quite like yours.
Can you tell us, though, why you have to have y if x == y? Is there
some subtle difference between the two equal objects?
~Ethan~
More information about the Python-list
mailing list