Steve Holden wrote:
> fraca7 wrote:
>
>> The memory allocation for integers is optimized. 'Small' integers
>> (between -5 and 100 IIRC) are allocated once and reused. The memory
>> for larger integers is allocated once and reused whenever possible, so
>> the malloc() overhead is negligible.
>
>
> The first bit's right, the second bit isn't:
>
> >>> id(12100)
> 4604168
> >>> id(121*100)
> 4604204
> >>>
>
FWIW, I read "whenever possible" not as "whenever theoretically
possible" but as "whenever the (comparatively simple) interpreter
recognizes that reuse is possible".
>>> a = 12100
>>> b = 12100
>>> a is b
False
>>> def f():
a = 12100
b = 12100
c = 121*100
print a is b
print a is c
>>> f()
True
False
>>>
The interpreter, when compiling the function, can recognize that the two
constants are identical, and makes them the same object. On the
interactive interpreter, or after a computation, the interpreter doesn't
bother to check to see if it already has the same value integer object.
(It could, but the overhead would likely swamp any savings.)
--
http://mail.python.org/mailman/listinfo/python-list
