# Benjamin

## python的pack和unpack用法

pack和unpack在处理二进制流中比较常用的封包、解包格式
#  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)
# 计算给定的格式(fmt)占用多少字节的内存
calcsize(fmt)
fmt格式为：
FORMATC TYPEPYTHON TYPESTANDARD SIZENOTES
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)

CHARACTERBYTE ORDERSIZEALIGNMENT
@ native native native
= native standard none
< little-endian standard none
> big-endian standard none
! network (= big-endian) standard none

unsigned short  id;
char[4] tag;
unsigned int  version;
unsigned int  count;

import  struct
id, tag, version, count =  struct.unpack("!H4s2I", s)

ss =  struct.pack("!H4s2I", id, tag, version, count);

解包
size, = struct.unpack('>H',raw[0:2])
cmd, = struct.unpack('>H', raw[2:4])
string, = struct.unpack('>{0}s'.format(size - 4), raw[4:size])

fmt = ">HH{0}s".format(len(result))
args = (len(result), cmd,result)
data = struct.pack(fmt, *args)

posted on 2019-09-21 17:30 Benjamin 阅读(27) 评论(0)  编辑 收藏 引用 所属分类: python