def xmlrpc_methodSignature(self, method):
        """
        Return a list of type signatures.

        Each type signature is a list of the form [rtype, type1, type2, ...]
        where rtype is the return type and typeN is the type of the Nth
        argument. If no signature information is available, the empty
        string is returned.
        """
        method = self._xmlrpc_parent.lookupProcedure(method)
        return getattr(method, 'signature', None) or ''

        Return a list of type signatures.

        Each type signature is a list of the form [rtype, type1, type2, ...]
        where rtype is the return type and typeN is the type of the Nth
        argument. If no signature information is available, the empty
        string is returned.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/xmlrpc.py