ctypes可变长度结构 [英] ctypes variable length structures

问题描述

自从我阅读Dave Beazley关于二进制I / O处理的帖子（http://dabeaz.blogspot.com/2009/08/python-binary-io-handling.html）以来，我一直想创建一个Python库对于特定的有线协议。但是，我找不到可变长度结构的最佳解决方案。这是我想做的事情：

Ever since I read Dave Beazley's post on binary I/O handling (http://dabeaz.blogspot.com/2009/08/python-binary-io-handling.html) I've wanted to create a Python library for a certain wire protocol. However, I can't find the best solution for variable length structures. Here's what I want to do:

import ctypes as c

class Point(c.Structure):
    _fields_ = [
        ('x',c.c_double),
        ('y',c.c_double),
        ('z',c.c_double)
        ]

class Points(c.Structure):
    _fields_ = [
        ('num_points', c.c_uint32),
        ('points', Point*num_points) # num_points not yet defined!
        ]

类积分由于尚未定义 num_points ，因此无法使用。一旦知道 num_points 后，我便可以重新定义 _fields _ 变量，但是由于它是一个类变量，因此会影响所有其他 Points 实例。

The class Points won't work since num_points isn't defined yet. I could redefine the _fields_ variable later once num_points is known, but since it's a class variable it would effect all of the other Points instances.

什么是解决此问题的pythonic解决方案？

What is a pythonic solution to this problem?

推荐答案

最简单的方法是使用您给出的示例在需要信息时定义结构。

The most straightforward way, with the example you gave is to define the structure just when you have the information you need.

一种简单的实现方法是在点，您将使用它，而不是在模块根目录下使用-例如，您可以将 class 主体放入函数中，该函数将充当工厂-我认为那是

A simple way of doing that is creating the class at the point you will use it, not at module root - you can, for example, just put the class body inside a function, that will act as a factory - I think that is the most readable way.

import ctypes as c



class Point(c.Structure):
    _fields_ = [
        ('x',c.c_double),
        ('y',c.c_double),
        ('z',c.c_double)
        ]

def points_factory(num_points):
    class Points(c.Structure):
        _fields_ = [
            ('num_points', c.c_uint32),
            ('points', Point*num_points) 
            ]
    return Points

#and when you need it in the code:
Points = points_factory(5)

对不起-
将为您填充值的C代码-不能回答它们。会以另一种方式发布。

Sorry - It is the C code that will "fill in" the values for you - that is not the answer them. WIll post another way.

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