python struct (对python obj进行编码解码)
参考文档：http://docs.python.org/2/library/struct.html
http://blog.163.com/ws__fyy/blog/static/12243381720123181013666/
http://blog.163.com/kongdelu2009@yeah/blog/static/1119952072009102562126194/
# -*- coding: utf-8 -*-
import struct
import sys
import os
'''
1. Byte order, Size, Alignment
-------------------------------------------------------------
Character Byte order Size Alignment
-------------------------------------------------------------
@ native native native==> default
= native standard none
< little-endian standard none
> big-endian standard none
! network (= big-endian) standard none
-------------------------------------------------------------
1). byte order: Native byte order is big-endian or little-endian, depending on the host system.
①Intel X86 / AMD64(x86-64) ==> little-endian
②Motorola 68000 / PowerPC G5 ==> big-endian
③ARM / Intel Itanium feature switchable endianness (bi-endian)
2). size:
①Native size are determined using the C compiler's sizeof expression.
②Standard size depends only on the 'format character'
3). alignment:
2. format character
Format C Type Python type Standard size
x pad byte no value
c char string of length 1 1
b signed char integer 1
B unsigned char integer 1
? _Bool bool 1
h short integer 2
H unsigned short integer 2
i int integer 4
I unsigned int integer 4
l long integer 4
L unsigned long integer 4
q long long integer 8
Q unsigned long longinteger 8
f float float 4
d double float 8
s char[] string
p char[] string
P void * integer
'''
#检查大端小端
print sys.byteorder
s='abcde'
a=20
b=400
'''
3. python obj-->pack-->str
'''
packed_str = struct.pack('< 5s2i',s,a,b)
#< : little endian, standard side, none alignment
# whitespaces are ignored.
#5s : 5 is the "size" of the string
#2i : 2 is the "repeat count"
#print len(s)
print struct.calcsize('< 5s2i')
print repr(s)
print type(s)
'''
4. str-->pack-->python obj
'''
(s, a, b) = struct.unpack('<5s2i', packed_str)
print s
print a
print b
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