python - 如何在 Python 中将 256 位大端整数转换为小端？

Question

不太复杂，或者我希望如此。我有一个 256 位十六进制整数编码为大端，我需要将其转换为小端。Python 的 struct 模块通常就足够了，但官方文档没有列出大小甚至接近我需要的格式。

使用 struct 的非长度特定类型（尽管我可能做错了）似乎不起作用：

>> x = 'ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000'
>> y = struct.unpack('>64s', x)[0] # Unpacking as big-endian
>> z = struct.pack('<64s', y) # Repacking as little-endian
>> print z
'ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000'

示例代码（应该发生什么）：

>> x = 'ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000'
>> y = endianSwap(x)
>> print y
'00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff'

Answer 1

该struct模块无法处理 256 位数字。因此，您必须手动进行编码。

首先，您应该将其转换为字节：

x = 'ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000'
a = x # for having more successive variables
b = a.decode('hex')
print repr(b)
# -> '\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\x00\x00\x00\x00'

这样您就可以使用@Lennart 的方法来反转它：

c = b[::-1]
# -> '\x00\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff'

d = c.encode('hex')
z = d
print z
# -> 00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff

Answer 2

>>> big = 'ffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000000'
>>> big[::-1]
'00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff'