def can_sign_txin(self, txin: 'TxInput', *, ignore_watching_only=False) -> bool:
        """Returns whether this keystore could sign this txin."""
        if not ignore_watching_only and self.is_watching_only():
            return False
        if not isinstance(txin, PartialTxInput):
            return False
        return bool(self._get_txin_derivations(txin))
Returns whether this keystore could sign this txin.
electrum/keystore.py