Raymond Hettinger wrote:
>> Hrvoje Niksic wrote:
>>> I've stumbled upon an oddity using sets. It's trivial to test if a
>>> value is in the set, but it appears to be impossible to retrieve a
>>> stored value,
>
> See: http://code.activestate.com/recipes/499299/
Thanks, this is *really* good, the kind of idea that seems perfectly
obvious once pointed out by someone else. :-) I'd still prefer sets to
get this functionality so they can be used to implement, say, interning,
but this is good enough for me.
In fact, I can derive from set and add a method similar to that in the
recipe. It can be a bit simpler than yours because it only needs to
support operations needed by sets (__eq__ and __hash__), not arbitrary
attributes.
class Set(set):
def find(self, item, default=None):
capt = _CaptureEq(item)
if capt in self:
return capt.match
return default
class _CaptureEq(object):
__slots__ = 'obj', 'match'
def __init__(self, obj):
self.obj = obj
def __eq__(self, other):
eq = (self.obj == other)
if eq:
self.match = other
return eq
def __hash__(self):
return hash(self.obj)
>>> s = Set([1, 2, 3])
>>> s.find(2.0)
2
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