a Structure impl support both ctypes and struct.

cstruct.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#  FileName    : cstruct.py
#  Author      : Feather.et.ELF <andelf@gmail.com>
#  Created     : Tue Feb 28 23:06:44 2012 by Feather.et.ELF
#  Copyright   : Feather Workshop (c) 2012
#  Description : mcpack v1 v2
#  Time-stamp: <2012-03-31 18:58:42 andelf>

import struct
import ctypes

class Structure(ctypes.Structure):
    def __init__(self, *args, **kwargs):
        if kwargs:
            if args:
                raise TypeError("can handle **kwargs and *args at a time.")
            ctypes.Structure.__init__(self, **kwargs)
        else:
            for i, field in enumerate(self._fields_):
                field_name = field[0]
                setattr(self, field_name, args[i])

    def to_str(self):
        fmt = ['=']
        values = []
        Ctype = ctypes.Array.__base__
        # from ctypes types to struct format
        field_map = {ctypes.c_char:   'c',
                     ctypes.c_uint8: 'B',
                     ctypes.c_uint16: 'H',
                     ctypes.c_uint32: 'I',
                     ctypes.c_ulong: 'L',
                     ctypes.c_ulonglong: 'Q',
                     ctypes.c_int8: 'b',
                     ctypes.c_int16: 'h',
                     ctypes.c_int32:  'i',
                     ctypes.c_long: 'l',
                     ctypes.c_longlong: 'q',
                     ctypes.c_float: 'f',
                     ctypes.c_double: 'd',
                     ctypes.c_bool: '?',
                     # add more here
                     }
        # special handling for array
        field_array_map = field_map.copy()
        field_array_map.update({ctypes.c_char: 's'})

        for key, tp in self._fields_:
            # construct fmt str
            if issubclass(tp, ctypes.Array):
                size = tp._length_
                orig_tp = tp._type_
                fmt.append("%d%s" % (size, field_array_map[orig_tp]))
            elif issubclass(tp, Ctype):
                fmt.append(field_map[tp])
            else:
                raise TypeError('Unkown type code: %s' % tp)
            values.append(getattr(self, key))

        fmt = ''.join(fmt)
        return struct.pack(fmt, *values)

    @classmethod
    def from_str(cls, string):
        assert len(string) == ctypes.sizeof(cls), \
            "string length error! not fit %d" % ctypes.sizeof(cls)
        buf = ctypes.create_string_buffer(string)
        inst = cls.from_buffer(buf)
        return inst

haven't support embed struct yet