New Construct Syntax

construct.py

import operator

import construct


class ConstructGetter(object):
    def __init__(self):
        self._index = 0

    def __getattr__(self, name):
        cons = getattr(construct, name)
        proxy = ConstructProxy(cons, self._index)
        self._index += 1
        return proxy


class ConstructProxy(object):
    def __init__(self, cons, index):
        self._cons = cons
        self._index = index
        self._args = []
        self._kwargs = {}

    def __call__(self, *args, **kwargs):
        self._args = args
        self._kwargs = kwargs
        return self

    def is_name_significant(self, name):
        return (name[0] != "_") or (not name[1:].isdigit())

    def get(self, name):
        if self.is_name_significant(name):
            return self._cons(name, *self._args, **self._kwargs)

        return self._cons(*self._args, **self._kwargs)


    def __cmp__(self, other):
        return cmp(self._index, other._index)


cs = ConstructGetter()


def subcons(**members):
    members = members.items()
    members = sorted(members, key=operator.itemgetter(1))
    members = [value.get(name) for name, value in members]
    return members


def struct(name, **members):
    return construct.Struct(name, *subcons(**members))


if __name__ == '__main__':
    s = struct("MyStruct",
               length=cs.UBInt8,
               data=cs.Bytes(lambda ctx: ctx["length"]),
               _1=cs.Padding(lambda ctx: 255 - ctx["length"])
    )

    print s.parse("\x0DHello, World!" + "\0" * 242)

    string = "Hello, World!"
    print repr(s.build(construct.Container(data=string, length=len(string))))