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= 比较:4字节bytearray转化为int =
{{{
Jacky <jacky.chao.wang@gmail.com>
to	"python-cn`CPyUG`华蟒用户组(中文Py用户组)" <python-cn@googlegroups.com>
cc	wileishn@gmail.com,
zoom.quiet@gmail.com
date	Mon, Aug 16, 2010 at 22:10
subject	方案比较：快速将4字节bytearray转化为int
}}}

##startInc
== 代码 ==
{{{#!python

import struct
import ctypes

def test_struct(buf, offset):
    return struct.unpack_from("I", buf, offset)[0]

def test_ctypes(buf, offset):
    return ctypes.c_uint32.from_buffer(buf, offset).value

def test_multi(buf, offset):
    return buf[offset] + (buf[offset+1] << 8) + (buf[offset+2] << 16) +(buf[offset+3] << 24)

buf_w = bytearray(5)
buf_w[1] = 1
buf_r = buffer(buf_w)

if __name__ == '__main__':
    import timeit
    t1 = timeit.Timer("test_struct(buf_r, 1)",
                   "from __main__ import test_struct, buf_r")
    t2 = timeit.Timer("test_ctypes(buf_w, 1)",
                   "from __main__ import test_ctypes, buf_w")
    t3 = timeit.Timer("test_multi(buf_w, 1)",
                   "from __main__ import test_multi, buf_w")
    print t1.timeit(number=1000)
    print t2.timeit(number=1000)
    print t3.timeit(number=1000)
}}}

=== 结果 ===
{{{

number = 10000
0.0081958770752
0.012549161911
0.0112121105194

number = 1000
0.00087308883667
0.00125789642334
0.00110197067261

number = 100
0.0000917911529541     # 9.17911529541e-05
0.000133991241455
0.00011420249939

number = 10
1.69277191162e-05
2.19345092773e-05
1.69277191162e-05

number = 1
1.00135803223e-05
1.00135803223e-05
5.96046447754e-06
}}}
为什么运行次数不同，结果也有差异呢？
 * 测试环境，ubuntu 10.04，我把number调到100w
 
##endInc

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创建 by -- ZoomQuiet [<<DateTime(2010-08-17T11:44:33+0800)>>]