qiskit/transpiler/layout.py
def is_virtual(value):
        """Checks if value has the format of a virtual qubit """
        return value is None or isinstance(value, tuple) and len(value) == 2 and isinstance(
            value[0], Register) and isinstance(value[1], int)
def is_virtual(value):
        """Checks if value has the format of a virtual qubit """
        return value is None or isinstance(value, tuple) and len(value) == 2 and isinstance(
            value[0], Register) and isinstance(value[1], int)
Checks if value has the format of a virtual qubit