[Tutor] Performance difference, ``in'' vs ``has_key()''

Andreas Kostyrka andreas at kostyrka.org
Mon Jul 18 01:52:31 CEST 2005

A short trial with timeit.py shows that

k in d is faster than d.has_key(k)

k in d is about as fast as hk(d), where hk = d.has_key

So it seems both expressions are about the same, but the expression
dict.has_key involves an additional dictionary lookup to fetch has_key.


Am Sonntag, den 17.07.2005, 11:18 -0700 schrieb Bill Campbell:
> I'm going to be doing some work where I'll be doing existence
> testings on keys on about a million records where it may require
> multiple passes so I'm a bit concerned about the timing of these
> tests.
> Is there any significant performance difference between the
> tests, ``key in dictionary'' and ``dictionary.has_key(key)''?
> I would prefer using the ``key in'' because it's a bit easier to
> type, and can also be used with lists in addition to dictionaries.
> A related question is where's the trade-off between using ``in''
> with a list, and a dictionary?  I presume that using it with
> small hashes will be faster than dictionries since it doesn't
> have to calculate the hashes.
> Bill
> --
> INTERNET:   bill at Celestial.COM  Bill Campbell; Celestial Software LLC
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