 import inspect, types, __builtin__

 ############## preliminary: two utility functions #####################

 def skip_redundant(iterable, skipset=None):
    "Redundant items are repeated items or items in the original skipset."
    if skipset is None: skipset = set()
    for item in iterable:
        if item not in skipset:
            skipset.add(item)
            yield item


 def remove_redundant(metaclasses):
    skipset = set([types.ClassType])
    for meta in metaclasses: # determines the metaclasses to be skipped
        skipset.update(inspect.getmro(meta)[1:])
    return tuple(skip_redundant(metaclasses, skipset))

 ##################################################################
 ## now the core of the module: two mutually recursive functions ##
 ##################################################################

 memoized_metaclasses_map = {}

 def get_noconflict_metaclass(bases, left_metas, right_metas):
     """Not intended to be used outside of this module, unless you know
     what you are doing."""
     # make tuple of needed metaclasses in specified priority order
     metas = left_metas + tuple(map(type, bases)) + right_metas
     needed_metas = remove_redundant(metas)

     # return existing confict-solving meta, if any
     if needed_metas in memoized_metaclasses_map:
       return memoized_metaclasses_map[needed_metas]
     # nope: compute, memoize and return needed conflict-solving meta
     elif not needed_metas:         # wee, a trivial case, happy us
         meta = type
     elif len(needed_metas) == 1: # another trivial case
        meta = needed_metas[0]
     # check for recursion, can happen i.e. for Zope ExtensionClasses
     elif needed_metas == bases: 
         raise TypeError("Incompatible root metatypes", needed_metas)
     else: # gotta work ...
         metaname = '_' + ''.join([m.__name__ for m in needed_metas])
         meta = classmaker()(metaname, needed_metas, {})
     memoized_metaclasses_map[needed_metas] = meta
     return meta

 def classmaker(left_metas=(), right_metas=()):
    def make_class(name, bases, adict):
        metaclass = get_noconflict_metaclass(bases, left_metas, right_metas)
        return metaclass(name, bases, adict)
    return make_class
