python pack和unpack的用法

#  按照给定的格式(fmt)，把数据封装成字符串(实际上是类似于c结构体的字节流)

pack(fmt, v1, v2, ...) 

# 按照给定的格式(fmt)解析字节流string，返回解析出来的tuple

unpack(fmt, string)   

=======================================

>>> import struct
>>> struct.pack('>H',56)
'\x008'

>>> struct.unpack('>H','\x008')
(56,)

>>> struct.unpack('>H','\x008')[0]
56

====================

>>> struct.pack('@H', 56)
'8\x00'
>>> struct.unpack('@H', '8\x00')
(56,)
>>>
 

=====================

fmt格式为：

FORMAT	C TYPE	PYTHON TYPE	STANDARD SIZE	NOTES
x	pad byte	no value
c	char	string of length 1	1
b	signed char	integer	1	(3)
B	unsigned char	integer	1	(3)
?	_Bool	bool	1	(1)
h	short	integer	2	(3)
H	unsigned short	integer	2	(3)
i	int	integer	4	(3)
I	unsigned int	integer	4	(3)
l	long	integer	4	(3)
L	unsigned long	integer	4	(3)
q	long long	integer	8	(2), (3)
Q	unsigned long long	integer	8	(2), (3)
f	float	float	4	(4)
d	double	float	8	(4)
s	char[]	string
p	char[]	string
P	void *	integer		(5), (3)

格式中的第一个字符来改变对齐方式(字节序).定义如下

CHARACTER	BYTE ORDER	SIZE	ALIGNMENT
@	native	native	native
=	native	standard	none
<	little-endian	standard	none
>	big-endian	standard	none
!	network (= big-endian)	standard	none