Peter Otten wrote:
> Leo Kislov wrote:
>
>> On Jun 13, 5:40 pm, [EMAIL PROTECTED] wrote:
>>> Hi all,
>>>
>>> I am running Python 2.5 on Feisty Ubuntu. I came across some code that
>>> is substantially slower when in a method than in a function.
>>>
>>> >>> cProfile.run("bar.readgenome(open('cb_foo'))")
>>>
>>> 20004 function calls in 10.214 CPU seconds
>>
>>> >>> cProfile.run("z=r.readgenome(open('cb_foo'))")
>>>
>>> 20004 function calls in 0.041 CPU seconds
>>>
>>
>> I suspect open files are cached so the second reader
>> picks up where the first one left: at the of the file.
>> The second call doesn't do any text processing at all.
>>
>> -- Leo
>
> Indeed, the effect of attribute access is much smaller than what the OP is
> seeing:
I have to take that back
> $ cat iadd.py
> class A(object):
> def add_attr(self):
> self.x = 0
> for i in xrange(100000):
> self.x += 1
> def add_local(self):
> x = 0
> for i in xrange(100000):
> x += 1
>
> add_local = A().add_local
> add_attr = A().add_attr
> $ python2.5 -m timeit -s 'from iadd import add_local' 'add_local()'
> 10 loops, best of 3: 21.6 msec per loop
> $ python2.5 -m timeit -s 'from iadd import add_attr' 'add_attr()'
> 10 loops, best of 3: 52.2 msec per loop
Iddo, adding integers is not a good model for the effect you are seeing.
Caching, while happening on the OS-level isn't, either.
As already mentioned in this thread there is a special optimization for
some_string += another_string
in the Python C-source. This optimization works by mutating on the C-level
the string that is immutable on the Python-level, and is limited to cases
where there are no other names referencing some_string. The statement
self.s += t
is executed internally as
tmp = self.s [1]
tmp += t [2]
self.s = tmp [3]
where tmp is not visible from the Python level. Unfortunately after [1]
there are two references to the string in question (tmp and self.s) so the
optimization cannot kick in.
Peter
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