Fredrik Lundh wrote:
> Sion Arrowsmith wrote:
>
>
>>>(you cannot really use "profile" to *benchmark* things written in Python
>>>either; the
>>>profiler tells you where a given program spends the time, not how fast it is
>>>in com-
>>>parision with other programs)
>>
>>Hmm. Playing around with timeit suggests that although split() *is*
>>faster than split("\t"), it's fractional, rather than the OP's four
>>times faster. Is the overhead of profile keeping track of calls in
>>Python getting in the way?
>
>
> correct.
>
>
>>And why can map() keep everything at the C level when the list com-
>
> > prehension can't?
>
> map is called with two Python objects (the str.split callable and the
> sequence object), while the list comprehension is turned into a byte-
> code loop that evaluates s.split for each item in the sequence; compare
> and contrast:
>
> >>> def func(a):
> .... return map(str.split, a)
> ....
> >>> dis.dis(func)
> 2 0 LOAD_GLOBAL 0 (map)
> 3 LOAD_GLOBAL 1 (str)
> 6 LOAD_ATTR 2 (split)
> 9 LOAD_FAST 0 (a)
> 12 CALL_FUNCTION 2
> 15 RETURN_VALUE
>
> >>> def func(a):
> .... return [s.split() for s in a]
> ....
> >>> dis.dis(func)
> 2 0 BUILD_LIST 0
> 3 DUP_TOP
> 4 STORE_FAST 1 (_[1])
> 7 LOAD_FAST 0 (a)
> 10 GET_ITER
> >> 11 FOR_ITER 19 (to 33)
> 14 STORE_FAST 2 (s)
> 17 LOAD_FAST 1 (_[1])
> 20 LOAD_FAST 2 (s)
> 23 LOAD_ATTR 0 (split)
> 26 CALL_FUNCTION 0
> 29 LIST_APPEND
> 30 JUMP_ABSOLUTE 11
> >> 33 DELETE_FAST 1 (_[1])
> 36 RETURN_VALUE
>
> (LOAD_GLOBAL and LOAD_ATTR does full name lookups, while LOAD_FAST loads
> a local variable using an integer index)
>
> </F>
>
Well I guess if people wanted to argue for keeping the functionals this
should be on the list ...
regards
Steve
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