一.c，ctypes和python的數據類型的對應關係
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) >>> c c_int(34) >>> c.value 34 >>> c.value=343 >>> c.value 343
3.操作字符串
>>> p=create_string_buffer(10) >>> p.raw 'x00x00x00x00x00x00x00x00x00x00' >>> p.value='fefefe' >>> p.raw 'fefefex00x00x00x00' >>> p.value='fefeeeeeeeeeeeeeeeeeeeeeee' #字符串太長，報錯 Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: string too long
4.操作指針
>>> i=c_int(999) >>> pi=pointer(i) >>> pi <__main__.LP_c_int object at 0x7f7be1983b00> >>> pi.value Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'LP_c_int' object has no attribute 'value' >>> pi.contents c_int(999) >>> pi.contents=c_long(34343) >>> pi.contents c_int(34343) 通過pointer獲取一個值的指針 通過contents獲取一個指針的值
5.c的結構體
#定義一個c的structure，包含兩個成員變量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) 定義一個類型為POINT的數組 >>> 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 "<stdin>", line 1, in <module> AttributeError: 'POINT_Array_3' object has no attribute 'y' >>> for i in pa:print i.y ... 3 4 5
6.訪問so文件
1.創建一個c文件
#include <stdio.h> int hello_world(){ printf("Hello World"); return 0; } int main(){ hello_world(); return 0; }
2.編譯成動態連結庫
gcc hello_world.c -fPIC -shared -o hello_world.so
3.python中調用庫中的函數
from ctypes import cdll c_lib=cdll.LoadLibrary('./hello_world.so') c_lib.hello_world()
二.測試c的性能和python的差別
sum.c
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; } 測試方案：計算1-100的和 測試次數：100萬次
1. 直接用c來執行，通linux 的time命令來記錄執行的用時
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(){ int i ; for (i=0;i<1000000;i++){ sum(100); } return 0; }
測試結果的例子：
real 1.16 user 1.13 sys 0.01
2.通過Python調用so文件和python的測試結果
sum_test.py:
def sum_python(num): s = 0 for i in xrange(1,num+1): s += i return s from ctypes import cdll c_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)
測試結果的例子
c 1.02756714821 python 7.90672802925
3.測試erlang的測試結果
剛剛學了erlang，那就一起測試一下erlang的運算性能
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).
調用：
timer:tc(sum,sum_test,[100,1000000]).
測試結果的例子：
{2418486,0}
4.測試結果
用上面的測試方法，進行10次測試，去除最大值和最小值，再計算平均值，得出：
單位：秒
求和的運行，使用的內存比較小，但是佔用CPU資源比較多。 原生的C是最快的，Python調用c會稍微慢一點，原因是計算100的和的操作是在c裡面做的，而執行100萬次的邏輯是在python做的 erlang的性能雖然比c稍慢，但是也是不錯的， Python的運行效率慘不忍睹。。。
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