How much slower is dict indexing vs. list indexing?

Emin emin.shopper at
Thu Jan 11 23:40:53 CET 2007

Dear Experts,

How much slower is dict indexing vs. list indexing (or indexing into a
numpy array)? I realize that looking up a value in a dict should be
constant time, but does anyone have a sense of what the overhead will
be in doing a dict lookup vs. indexing into a list? Some ad hoc tests
I've done indicate that the overhead is less than 15% (i.e., dict
lookups seem to take no more than 15% longer than indexing into a list
and there doesn't seem to be much difference in indexing into a list
vs. a numpy array).

The reason I ask is because I'm wondering how hard I should work to
compute and store an index into a list to avoid repeated hash table
lookups. From my tests, it looks like the answer is basically "don't
bother". Does anyone have information, thoughts, or comments on this?


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