python 字节序

阮一峰 - 理解字节序

获取字节顺序

import sys

endianness = sys.byteorder
print("system Endianness is "+ endianness)

大小端转换

"6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000".decode('hex')[::-1].encode('hex_codec') 
# => 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

import struct

ver = 1
prev_block = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"
mrkl_root = "0e3e2357e806b6cdb1f70b54c3a3a17b6714ee1f0e68bebb44a74b1efd512098"
time = 1231469665
bits = 486604799
nonce = 2573394689

struct.pack("<L", ver) #转换为 unsigned long型小端
prev_block.decode('hex')[::-1] # 转换为16进制并大小端转换
mrkl_root.decode('hex')[::-1] # 转换为16进制并大小端转换
struct.pack("<LLL", time, bits, nonce) # 把3个变量转换为 unsigned long型小端

struct

在struct中有以下几种字节顺序

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

字符	字节顺序	尺寸	对齐方式
@	本机	本机	本机
=	本机	标准	无
<	小端	标准	无
>	大端	标准	无
！	网络即大端	标准	无

数据格式

Format	C Type	Python type	Standard size	Notes
x	pad byte	no value
c	char	bytes of length 1	1
b	signed char	integer	1	(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)
n	ssize_t	integer		(4)
N	size_t	integer		(4)
e	(7)	float	2	(5)
f	float	float	4	(5)
d	double	float	8	(5)
s	char[]	bytes
p	char[]	bytes
P	void *	integer		(6)

字符	C类型	python类型	标准尺寸
x	填充字节	没有意义的值
c	char	长度为1的字节	1
b	signed char	整型	1
B	unsigned char	整型	1
？	_Bool	布尔	1
h	short	整型	2
H	unsigned short	整型	2
i	int	整型	4
I	unsigned int	整型	4
l	long	整型	4
L	unsigned long	整型	4
q	long long	整型	8
Q	unsigned long long	整型	8
n	ssize_t	整型
N	size_t	整型
e		浮动	2
f	float	浮动	4
d	double	浮动	8
s	char[]	字节
p	char[]	字节
P	void *	整型

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参考:

https://en.wikipedia.org/wiki/Endianness
https://docs.python.org/3/library/struct.html
https://blog.csdn.net/youand_me/article/details/78890316
https://stackoverflow.com/questions/7869752/javascript-typed-arrays-and-endianness