Egor> i know how to get item by key ... Egor> but i wonder how to get key by item
Assuming your dictionary defines a one-to-one mapping, just invert it:
>>> forward = {10 : 50, 2 : 12, 4 : 43} >>> reverse = dict([(v,k) for (k,v) in forward.iteritems()]) >>> print forward {10: 50, 4: 43, 2: 12} >>> print reverse {50: 10, 43: 4, 12: 2}
That doubles your storage, so you'll have to trade that off against the speed gain of not having to loop over the entire dictionary.
Skip
But beware that all the items in the original dictionary must be hashable. The example shows just integers, so I assume they are in this case. But generally, this may not work.
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