def copy(self):
            'New ChainMap or subclass with a new copy of maps[0] and refs to maps[1:]'
            return self.__class__(self.maps[0].copy(), *self.maps[1:])
New ChainMap or subclass with a new copy of maps[0] and refs to maps[1:]
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_vendor/distlib/compat.py