On Sun, 23 Mar 2008 10:45:38 -0700, Paul Rubin wrote:
> John Nagle <[EMAIL PROTECTED]> writes:
>> What's the cheapest way to test for an empty dictionary in Python?
>>
>> if len(dict.keys() > 0) :
>
> I like to think len(dict) is constant time but I haven't checked the
> code. Same for bool(dict) (which is what you get when you run "if dict:
> ...").
Except that "if dict" doesn't needlessly and wastefully create a bool.
>>> from timeit import Timer
>>> Timer("if {1:2}: pass").timeit()
1.1590199184417725
>>> Timer("if bool({1:2}): pass").timeit()
1.8825540542602539
Python knows the truth value of built-in types like dicts without
actually converting them to bools, or for that matter calling __len__ or
__nonzero__ on them.
--
Steven
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