ctypes variable length structures

Question

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

Answer 1

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

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)

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