def get_file_to_edit(self):
        # type: () -> Optional[str]
        """Returns the file with highest priority in configuration
        """
        assert self.load_only is not None, \
            "Need to be specified a file to be editing"

        try:
            return self._get_parser_to_modify()[0]
        except IndexError:
            return None
Returns the file with highest priority in configuration
        
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_internal/configuration.py