Two functions to glue python objects together

oocollage.py

#!/usr/bin/env python
# -*-coding: utf8-*-
# Terms of the MIT license, which apply to this software
# ========================================================
# Copyright (C) 2014 Eric Ringeisen
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__version__ = '2014.06.12'
__doc__ = '''oocollage

This module defines a function `collage()` which purpose is to create
superobjects by gluing existing python objects together.

Another function `collage_class()` returns a base class for such
superobjects, allowing further specialization of these objects.

Example:
    >>> class Lion(object):
    ...     def hunt(self):
    ...             print("I'm hunting")
    ... 
    >>> class Duck(object):
    ...     def quack(self):
    ...             print("Quack! Quack!")
    ... 
    >>> class Fish(object):
    ...     def swim(self):
    ...             print("I'm swimming")
    ... 
    >>> lion = Lion()
    >>> duck = Duck()
    >>> fish = Fish()
    >>> monster = collage(lion, duck, fish)
    >>> monster.hunt()
    I'm hunting
    >>> monster.swim()
    I'm swimming
    >>> monster.quack()
    Quack! Quack!
    >>>
    >>> ldf_type = collage_class(lion, duck, fish)
    >>> class UserMonster(ldf_type):
    ...     def go(self):
    ...         self.hunt()
    ...         self.quack()
    ...         self.swim()
    ...
    >>> m = UserMonster()
    >>> m.go()
    I'm hunting
    Quack! Quack!
    I'm swimming

'''
import itertools as itt


def linearize(items):
    ### C3 linearization algorithm adapted to our case.
    ### https://www.python.org/download/releases/2.3/mro/
    items = list(items)
    for i, x in enumerate(items):
        if isinstance(x, BaseCollage):
            items[i] = x._collage_mro
        else:
            items[i] = (x,)
    return tuple(_c3_merge(items))
        
def _c3_merge(seqs):
    seqs = [x for x in seqs if x]
    while seqs:
        # find head
        s = set(itt.chain.from_iterable(L[1:] for L in seqs))
        x = itt.dropwhile(lambda pair: pair[1][0] in s, enumerate(seqs))
        try:
            i, item = next(x)
        except StopIteration:
            raise RuntimeError("Impossible C3 linearization in ObjectCollage creation")
        item = item[0]
        yield item
        seqs[:] = [tuple(x for x in L if x != item) for L in seqs]
        seqs = [x for x in seqs if x]

class BaseCollage(object):
    def __getattr__(self, attr):
        for n in self._collage_mro:
            try:
                # print("trying", n, attr)
                return getattr(n, attr)
            except AttributeError:
                pass
        raise AttributeError(attr)

def collage_class(*items):
    class Collage(BaseCollage):
        _collage_mro = linearize(items)
    return Collage

def collage(*items):
    return collage_class(*items)()

if __name__ == '__main__':
    import doctest
    doctest.testmod()