尝试保存字节序时，Python struct.pack() 'struct.error: bad char in struct format' [英] Python struct.pack() 'struct.error: bad char in struct format' when trying to save endianess

问题描述

我正在尝试打包一个字符串和一个字符串的长度.

I am trying to pack a string and the length of a string.

fmt = '<P' + str(len(string)) + 'p'

这导致我出错:struct.error: bad char in struct format而，做

This leads me to an error : struct.error: bad char in struct format Whereas, doing

fmt = 'P' + str(len(string))+'p'

不会给我一个错误.我无法理解为什么会发生这种情况，我的理解是指定 '<'无论本机机器如何，一开始都会使其成为小端.

Does not give me an error. I am unable to understand why this happens, my understanding is that specifying '<' at the start will make it little endian regardless of the native machine.

推荐答案

来自 struct 模块文档字符串:

From the struct module docstring:

The remaining chars indicate types of args and must match exactly;
...
Special case (only available in native format):
  P:an integer type that is wide enough to hold a pointer.

所以当你使用P格式时你不能修改endianess；它仅以原生格式提供.

So you can't modify the endianess when you use the P format; it is only available in native format.

另见此处的注释 5:https://docs.python.org/2/library/struct.html#format-characters

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