How to handle results of qml.expval

PennyLane Help Code Together
1

The result of qml.expval, qml.sample and qml.probs are objects of ‘ExpectationMP’ type which can not converted into np.array. FOr instance, here in "I.10 What did you expect? " of Pennylane codebook, how can I store results into numpy array;

# An array to store your results
shot_results = []

# Different numbers of shots
shot_values = [100, 1000, 10000, 100000, 1000000]

def fun(shoot):
    dev = qml.device('default.qubit' , wires =1 ,shots=shoot)
    qml.qnode(dev)
    qml.RX(np.pi/4 , 0)
    qml.Hadamard(0)
    qml.PauliZ(0)
    # STORE RESULT IN SHOT_RESULTS ARRAY
    return qml.expval(qml.PauliY(0))

for shots in shot_values: 
    ##################
    # YOUR CODE HERE #
    ##################

    # CREATE A DEVICE, CREATE A QNODE, AND RUN IT
    for shoot in shot_values:
        shot_results.append(fun(shoot)) # I got Error: 'ExpectationMP' object has no attribute 'numpy'

print(qml.math.unwrap(shot_results))
2

Hi @Afrah, welcome to our community!

I noticed that you defined “fun” outside of the “for” loop. This will cause problems.
The original question looked like the following:

# An array to store your results
shot_results = []
# Different numbers of shots
shot_values = [100, 1000, 10000, 100000, 1000000]
for shots in shot_values: 
    ##################
    # YOUR CODE HERE #
    ##################
    # CREATE A DEVICE, CREATE A QNODE, AND RUN IT
    # STORE RESULT IN SHOT_RESULTS ARRAY
    
print(qml.math.unwrap(shot_results))

Note that you only needed to add code inside the for shots in shot_values:

Also, in your code I see that you added another for shots in shot_values: within the original one so this will cause problems too.

I hope this can help you get going.