def initial_mapping(self, circuit: cirq.AbstractCircuit) -> dict[cirq.Qid, cirq.Qid]:
        """Returns the hard-coded initial mapping.

        Args:
            circuit: the input circuit with logical qubits.

        Returns:
            the hard-codded initial mapping.

        Raises:
            ValueError: if the qubits in circuit are not a subset of the qubit keys in the mapping.
        """
        if not circuit.all_qubits().issubset(set(self._map.keys())):
            raise ValueError("The qubits in circuit must be a subset of the keys in the mapping")
        return self._map
Returns the hard-coded initial mapping.

        Args:
            circuit: the input circuit with logical qubits.

        Returns:
            the hard-codded initial mapping.

        Raises:
            ValueError: if the qubits in circuit are not a subset of the qubit keys in the mapping.
        
cirq-core/cirq/transformers/routing/initial_mapper.py