def new_child(self, m=None):                # like Django's Context.push()
        if m is None:
            m = {}
        return self.__class__(m, *self.maps)
New ChainMap with a new map followed by all previous maps. If no
dataset/ETHPy150Open ionelmc/python-aspectlib/src/aspectlib/py2chainmap.py/ChainMap.new_child