How to use the pennylane.PauliZ function in PennyLane

def circuit(w, x=None):
            qml.RX(x[0], wires=[0])
            qml.RX(x[1], wires=[1])
            return qml.expval(qml.PauliZ(0)), qml.expval(qml.PauliZ(1))

def circuit(a):
            qml.RX(a, wires=0)
            return qml.var(qml.PauliZ(0))

def circuit(x):
            qml.Rot(0.3, x, -0.2, wires=[0])
            return qml.expval(qml.PauliZ(0))

def circuit(w, x=None):
            qml.RX(x, wires=[0])
            return qml.expval(qml.PauliZ(0))

def circuit():
            return qml.sample(qml.PauliZ(0)), qml.sample(qml.PauliZ(1)), qml.sample(qml.PauliZ(2))

def circuit():
            qml.BasisState(np.array([1, 0, 1]), wires=[0, 1, 2])
            op(wires=[0, 1, 2])
            return qml.expval(qml.PauliZ(0)), qml.expval(qml.PauliZ(1)), qml.expval(qml.PauliZ(2))

def circuit1(x):
            qml.RX(x, wires=0)
            qml.CRX(x, wires=[0, 1])
            return qml.expval(qml.PauliZ(0))

def ansatz(x, y, z):
            qml.QubitStateVector(np.array([1, 0, 1, 1])/np.sqrt(3), wires=[0, 1])
            qml.Rot(x, y, z, wires=0)
            qml.CNOT(wires=[0, 1])
            return qml.expval(qml.PauliZ(0)), qml.expval(qml.PauliY(1))

def circuit(phi=None):
    # Encoding of 4 classical input values
    for j in range(4):
        qml.RY(np.pi * phi[j], wires=j)

    # Random quantum circuit
    RandomLayers(rand_params, wires=list(range(4)))

    # Measurement producing 4 classical output values
    return [qml.expval(qml.PauliZ(j)) for j in range(4)]

def circuit2(phi1, phi2):
    qml.RX(phi1, wires=0)
    qml.RY(phi2, wires=0)
    return qml.expval(qml.PauliZ(0))