我一直对开销感兴趣,所以我写了一个最小的C扩展程序,导出了两个函数nop
和starnop
,它们几乎什么都不做,只是通过它们的输入(这两个相关的函数位于顶部,其余的只是乏味的样板代码):
amanmodule.c:
#include <Python.h>
static PyObject* aman_nop(PyObject *self, PyObject *args)
{
PyObject *obj;
if (!PyArg_UnpackTuple(args, "arg", 1, 1, &obj))
return NULL;
Py_INCREF(obj);
return obj;
}
static PyObject* aman_starnop(PyObject *self, PyObject *args)
{
Py_INCREF(args);
return args;
}
static PyMethodDef AmanMethods[] = {
{"nop", (PyCFunction)aman_nop, METH_VARARGS,
PyDoc_STR("nop(arg) -> arg\n\nReturn arg unchanged.")},
{"starnop", (PyCFunction)aman_starnop, METH_VARARGS,
PyDoc_STR("starnop(*args) -> args\n\nReturn tuple of args unchanged")},
{NULL, NULL}
};
static struct PyModuleDef amanmodule = {
PyModuleDef_HEAD_INIT,
"aman",
"aman - a module about nothing.\n\n"
"Provides functions 'nop' and 'starnop' which do nothing:\n"
"nop(arg) -> arg; starnop(*args) -> args\n",
-1,
AmanMethods
};
PyMODINIT_FUNC
PyInit_aman(void)
{
return PyModule_Create(&amanmodule);
}
setup.py:
from setuptools import setup, extension
setup(name='aman', version='1.0',
ext_modules=[extension.Extension('aman', ['amanmodule.c'])],
author='n.n.',
description="""aman - a module about nothing
Provides functions 'nop' and 'starnop' which do nothing:
nop(arg) -> arg; starnop(*args) -> args
""",
license='public domain',
keywords='nop pass-through identity')
接下来,我会将它们与纯Python实现以及一些几乎什么都不做的内置函数进行时间比较:
import numpy as np
from aman import nop, starnop
from timeit import timeit
def mnsd(x): return '{:8.6f} \u00b1 {:8.6f} \u00b5s'.format(np.mean(x), np.std(x))
def pnp(x): x
globals={}
for globals['nop'] in (int, bool, (0).__add__, hash, starnop, nop, pnp, lambda x: x):
print('{:60s}'.format(repr(globals['nop'])),
mnsd([timeit('nop(1)', globals=globals) for i in range(10)]),
' ',
mnsd([timeit('nop(True)',globals=globals) for i in range(10)]))
第一个问题,我的方法论没有什么愚蠢的地方吧?
每个1,000,000次调用的10个块的结果:
<class 'int'> 0.099754 ± 0.003917 µs 0.103933 ± 0.000585 µs
<class 'bool'> 0.097711 ± 0.000661 µs 0.094412 ± 0.000612 µs
<method-wrapper '__add__' of int object at 0x8c7000> 0.065146 ± 0.000728 µs 0.064976 ± 0.000605 µs
<built-in function hash> 0.039546 ± 0.000671 µs 0.039566 ± 0.000452 µs
<built-in function starnop> 0.056490 ± 0.000873 µs 0.056234 ± 0.000181 µs
<built-in function nop> 0.060094 ± 0.000799 µs 0.059959 ± 0.000170 µs
<function pnp at 0x7fa31c0512f0> 0.090452 ± 0.001077 µs 0.098479 ± 0.003314 µs
<function <lambda> at 0x7fa31c051378> 0.086387 ± 0.000817 µs 0.086536 ± 0.000714 µs
现在我的实际问题是:即使我的nops是用C编写的并且什么也不做(
starnop
甚至不解析它的参数),内置函数hash
仍然更快。我知道在Python中,整数是它们自己的哈希值,所以hash
在这里也是一个nop,但它并不比我的nops更慢,那么为什么会有速度差异呢?更新:完全忘记了:我在一个相当标准的x86_64机器上,linux gcc4.8.5。我使用
python3 setup.py install --user
安装扩展程序。