def __getitem__(self, key):
        for mapping in self.maps:
            try:
                return mapping[key]             # can't use 'key in mapping' with defaultdict
            except __HOLE__:
                pass
        return self.__missing__(key)            # support subclasses that define __missing__
dataset/ETHPy150Open ionelmc/python-aspectlib/src/aspectlib/py2chainmap.py/ChainMap.__getitem__