[Tutor] Style question with classes and modules
kent37 at tds.net
Thu Jul 19 23:51:33 CEST 2007
Terry Carroll wrote:
> On Thu, 19 Jul 2007, Kent Johnson wrote:
>> Attribute lookup seems to have gotten better since Beazley wrote; here
>> is a test program that uses three ways to access math.sqrt - module
>> attribute, global name, local name. Note that in the third version, all
>> three names (sqrt, d, i) are local:
> . . .
>> Sample output:
> I'm surprised the difference between the second and third versions is so
> dramatic. I get a result consistent with that (although you obviously
> have a much faster CPU than I!).
> Why is that so much faster? A smaller namespace to look through? Or the
> search being short-cut by finding in in the local space and therefore not
> needing to search the global? Something else?
Two reasons, IIUC:
- the search is short-cut by finding the name in the local space.
- I'm pretty sure that local names are allocated in an *array* on the
call stack, not in a dict, so access to local names is very fast - just
a fixed offset into an array, no hashing and other overhead of
This is such a common optimization that Raymond Hettinger (the king of
speed :-) wrote a decorator to do it automatically:
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