是否有Python映射链？

from UserDict import DictMixin

class Map(object, DictMixin):
    def __init__(self, *maps):
        self.maps = maps
    def __getitem__(self, key):
        for m in self.maps:
            if key in m:
                return m[key]
    def keys(self):
        return list(self.iterkeys())
    def iterkeys(self):
        return (k for m in self.maps for k in m.iterkeys())
    def values(self):
        return list(self.itervalues())
    def itervalues(self):
        return (v for m in self.maps for v in m.itervalues())

def glue(*maps):
    return Map(*maps)

M1 = {\'blah\': 1}
M2 = {\'duh\': 2}

M = glue(M1, M2)
print M[\'blah\']
print M[\'duh\']
print list(M.keys())
print list(M.values())

1
2
[\'blah\', \'duh\']
[1, 2]