Python调用C模块以及性能分析-白红宇

Python调用C模块以及性能分析

阅读量：6184 次

发布时间：2019-06-21

本文共 4055 字，大约阅读时间需要 13 分钟。

一.c，ctypes和python的数据类型的对应关系

ctypes type ctype Python type

c_char char 1-character string

c_wchar wchar_t 1-character unicode string

c_byte char int/long

c_ubyte unsigned char int/long

c_short short int/long

c_ushort unsigned short int/long

c_int int int/long

c_uint unsigned int int/long

c_long long int/long

c_ulong unsigned long int/long

c_longlong __int64 or long long int/long

c_ulonglong unsigned __int64 or unsigned long long int/long

c_float float float

c_double double float

c_char_p char * (NUL terminated) string or None

c_wchar_p wchar_t * (NUL terminated) unicode or None

c_void_p void * int/long or None

2.操作int

>>> from ctypes import *>>> c=c_int(34)>>> cc_int(34)>>> c.value34>>> c.value=343>>> c.value343

3.操作字符串

>>> p=create_string_buffer(10)>>> p.raw'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'>>> p.value='fefefe'>>> p.raw'fefefe\x00\x00\x00\x00'>>> p.value='fefeeeeeeeeeeeeeeeeeeeeeee'  #字符串太长，报错Traceback (most recent call last):  File "
    
     ", line 1, in 
     
      ValueError: string too long

4.操作指针

>>> i=c_int(999)>>> pi=pointer(i)>>> pi<__main__.LP_c_int object at 0x7f7be1983b00>>>> pi.valueTraceback (most recent call last):  File "
    
     ", line 1, in 
     
      AttributeError: 'LP_c_int' object has no attribute 'value'>>> pi.contentsc_int(999)>>> pi.contents=c_long(34343)>>> pi.contentsc_int(34343)

通过pointer获取一个值的指针

通过contents获取一个指针的值

5.c的结构体

#定义一个c的structure，包含两个成员变量x和y>>> class POINT(Structure):...     _fields_=[('x',c_int),('y',c_int)]... >>> point=POINT(2,4)>>> point<__main__.POINT object at 0x7f7be1983b90>>>> point.x,point.y(2, 4)>>> porint=POINT(y=2)>>> porint<__main__.POINT object at 0x7f7be1983cb0>>>> point=POINT(y=2) >>> point.x,point.y(0, 2)定义一个类型为POINT的数组>>> POINT_ARRAY=POINT*3>>> pa=POINT_ARRAY(POINT(2,3),POINT(2,4),POINT(2,5))>>> for i in pa:print pa.y... Traceback (most recent call last):  File "
    
     ", line 1, in 
     
      AttributeError: 'POINT_Array_3' object has no attribute 'y'>>> for i in pa:print i.y ... 345

6.访问so文件

1.创建一个c文件

#include 
    
     int hello_world(){    printf("Hello World\n");    return 0;}int main(){        hello_world();        return 0;}

2.编译成动态链接库

gcc hello_world.c  -fPIC -shared -o hello_world.so

3.python中调用库中的函数

from ctypes import cdllc_lib=cdll.LoadLibrary('./hello_world.so')c_lib.hello_world()

二.测试c的性能和python的差别

sum.c

#include <stdio.h>

int sum(int num){    long sum=0;    int i =0;    for( i=1;i<=num;i++){        sum=sum+i;    };    return sum;}int main(){    printf("%d",sum(10));    return 0;}

测试方案：计算1-100的和

测试次数：100万次

1. 直接用c来执行，通linux 的time命令来记录执行的用时
sum.c：

#include 
    
         int sum(int num){        long sum=0;        int i =0;        for( i=1;i<=num;i++){            sum=sum+i;        };        return sum;    }    int main(){        int i ;        for (i=0;i<1000000;i++){        sum(100);        }        return 0;

测试结果的例子：

real 1.16user 1.13sys 0.01

2.通过Python调用so文件和python的测试结果

sum_test.py:

def sum_python(num):    s = 0    for i in xrange(1,num+1):        s += i    return sfrom ctypes import cdllc_lib = cdll.LoadLibrary('./sum.so')def sum_c(num):    return c_lib.sum(num)def test(num):    import timeit    t1 = timeit.Timer('c_lib.sum(%d)' % num, 'from __main__ import c_lib')    t2 = timeit.Timer('sum_python(%d)' % num, 'from __main__ import sum_python')    print 'c', t1.timeit(number=1000000)    print 'python', t2.timeit(number=1000000)if __name__ == '__main__':    test(100)

测试结果的例子

c 1.02756714821python 7.90672802925

3.测试erlang的测试结果

刚刚学了erlang，那就一起测试一下erlang的运算性能

sum.erl:

-module(sum).-export([sum/2,sum_test/2]).sum(0,Sum) ->         Sum;sum(Num,Sum) ->        sum(Num-1,Sum+Num).sum_test(Num,0) ->        0;sum_test(Num,Times) ->        sum(Num,0),        sum_test(Num,Times-1).

调用：