On Thu, 08 Mar 2007 09:20:20 +0100, Alexander Eisenhuth wrote:
> Hello,
>
> what algo do you use, when you want to find the dict values from d, with
> members
> of l. Following example:
>
> >>> d = {1:2,2:3,3:4,4:5,5:6,6:7,7:8,8:9,9:10}
> >>> l = [7,8]
> >>> found_dic_members = <yourCode>
> >>> print found_dict_members
> [8,9]
It depends.
If all of the values in d are usable as keys (that is, all the values
are hashable, so no lists or sets etc.) then you can build a
reverse-lookup dictionary and use that for fast look-ups.
>>> d = {1: 'a', 2: 'b', 3: 'c'}
>>> rd = dict(zip(d.values(), d.keys()))
>>> rd
{'a': 1, 'c': 3, 'b': 2}
But if you can't do that, you're stuck with a slow search through the
entire dict:
def reverse_search(d, target):
"""Return the first key of dict d that matches the target value."""
for key, value in d.iteritems():
if value == target:
return key
raise KeyError('no key found matching that value')
In both cases though, you have to think about what you want to happen for
duplicated values.
--
Steven D'Aprano
--
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