def _pauli_expansion_(self) -> value.LinearDict[str]:
        """Efficiently obtains expansion of self in the Pauli basis.

        Returns:
            Linear dict keyed by name of Pauli basis element. The names
            consist of n captal letters from the set 'I', 'X', 'Y', 'Z'
            where n is the number of qubits. For example, 'II', 'IX' and
            'XY' are valid Pauli names in the two-qubit case.
        """
Efficiently obtains expansion of self in the Pauli basis.

        Returns:
            Linear dict keyed by name of Pauli basis element. The names
            consist of n captal letters from the set 'I', 'X', 'Y', 'Z'
            where n is the number of qubits. For example, 'II', 'IX' and
            'XY' are valid Pauli names in the two-qubit case.
        
cirq-core/cirq/protocols/pauli_expansion_protocol.py