struct模块简介

struct简介

使用struct可以在python数值和C的结构之间进行转换,表示方式为Python strings. 一般用于处理文件中的二进制数据(如:BMP图片)或是网络连接中的报文(如:OSPF, EIGRP报文内容)

方法:

struct.pack(fmt, v1, v2, ...) 根据fmt规定的格式对v1, v2, ...内容进行打包, 并返回打包(转换)后的字节码.

struct.pack_into(fmt, buffer, offset, v1, v2, ...) 根据fmt规定的格式对v1, v2, ...内容进行打包, 然后将打包后的内容写入buffer中offset位置.

struct.unpack(fmt, string)根据fmt规定的格式对string(其实是字节码)进行unpack(解码), 并以元组的形式返回解码内容.

struct.unpack_from(fmt, buffer[, offset=0])对buffer中offset位置起始的内容根据fmt进行解码,并将结果以元组形式返回.

struct.calcsize(fmt) 返回fmt指定的格式转换后的数据长度(unit: Byte)

格式参数: fmt

Order Character

Character	Byte order	Size	Alignment
@	native	native	native
=	native	standard	none
<	little-endian	standard	none
>	big-endian	standard	none
!	network(= big-endian)	standard	none

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 long	integer	8
f	float	float	4
d	double	float	8
s	char[]	string
p	char[]	string
P	void *	integer

Examples

Construct the first part of an IP packet

import struct
#69 is  Version and IHL, 0 is TOS, 1420 is Total Length
first_line = struct.pack('>BBH', 69, 0, 1420)  
print(first_line)
> b'E\x00\x05\x8c'

#calculate the length of format '>BBH'
struct.calcsize('>BBH')
> 4   

Unpack a string according to the format character

import struct
s1 = b'E\x00\x05\x8c'
#unpack the string s1 (s1 is Bytes) according to format '>BBH'
result = struct.unpack('>BBH', s1)
print(result)
>(69, 0, 1420)