def getsig_by_symbol_name(self, name: str) -> Signature:
        """ Retrieve the unique Signature of a symbol.
        Fail if the Signature is not unique
        """
        subscope = self.get_by_symbol_name(name)
        if len(subscope) != 1:
            raise KeyError("%s have multiple candidates in scope" % name)
        v = list(subscope.values())
        return v[0]
Retrieve the unique Signature of a symbol.
        Fail if the Signature is not unique