python struct笔记

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http://firefish.blog.51cto.com/298258/112690

http://python.jobbole.com/81554/

https://zhidao.baidu.com/question/1369339939501292219.html

index += struct.calcsize('>IIII')

然后使用struc.unpack_from
'>IIII'是说使用大端法读取4个unsinged int32

然后读取一个图片测试是否读取成功

'>784B'的意思就是用大端法读取784个unsigned byte

>>> import struct
>>> a=20
>>> b=400
>>> str=struct.pack('ii',a,b) #转换成字节流，虽然还是字符串，但是可以在网络上传输
>>> print len(str) #ii 表示两个int
8 #可以看到长度为8个字节，正好是两个int型数据的长度
>>> print str
#二进制是乱码
>>> print repr(str)
'\x14\x00\x00\x00\x90\x01\x00\x00' #其中十六进制的 0x00000014, 0x00001009分别表示20和400
>>>

http://blog.csdn.net/stonesharp/article/details/32685159

学习例子:

# ref: http://blog.csdn.net/JGood/archive/2009/06/22/4290158.aspx
import struct
#pack - unpack
print
print '===== pack - unpack ====='
str = struct.pack("ii", 20, 400)
print 'str:', str
print 'len(str):', len(str) # len(str): 8
a1, a2 = struct.unpack("ii", str)
print "a1:", a1 # a1: 20
print "a2:", a2 # a2: 400
print 'struct.calcsize:', struct.calcsize("ii") # struct.calcsize: 8
#unpack
print
print '===== unpack ====='
string = 'test astring'
format = '5s 4x 3s'
print struct.unpack(format, string) # ('test ', 'ing')
string = 'he is not very happy'
format = '2s 1x 2s 5x 4s 1x 5s'
print struct.unpack(format, string) # ('he', 'is', 'very', 'happy')
#pack
print
print '===== pack ====='
a = 20
b = 400
str = struct.pack("ii", a, b)
print 'length:', len(str) #length: 8
print str
print repr(str) # '/x14/x00/x00/x00/x90/x01/x00/x00'
#pack_into - unpack_from
print
print '===== pack_into - unpack_from ====='
from ctypes import create_string_buffer
buf = create_string_buffer(12)
print repr(buf.raw)
struct.pack_into("iii", buf, 0, 1, 2, -1)
print repr(buf.raw)
print struct.unpack_from("iii", buf, 0)

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