def addChecker(self, checker):
        """
        Add the checker specified.  If any checkers are added, the default
        checkers are automatically cleared and the only checkers will be the
        specified one(s).
        """
        if self._usingDefaultAuth:
            self['credCheckers'] = []
            self['credInterfaces'] = {}
            self._usingDefaultAuth = False
        super(Options, self).addChecker(checker)

        Add the checker specified.  If any checkers are added, the default
        checkers are automatically cleared and the only checkers will be the
        specified one(s).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/tap.py