def popitem(self):
            'Remove and return an item pair from maps[0]. Raise KeyError is maps[0] is empty.'
            try:
                return self.maps[0].popitem()
            except KeyError:
                raise KeyError('No keys found in the first mapping.')
Remove and return an item pair from maps[0]. Raise KeyError is maps[0] is empty.
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_vendor/distlib/compat.py