why ModuleNotFoundError: No module named 'qiskit.opflow' occured?

Question

i installed version 1.1 of qiskit. i don't have any idea why i can't able to use opflow module. this is the line i have error from qiskit.opflow import Gradient, StateFn, CircuitStateFn, Z

and this error occured in google colab:

> ModuleNotFoundError                       Traceback (most recent call last)
<ipython-input-2-1eb6f7fd39a6> in <cell line: 11>()
      9 from qiskit.circuit import ParameterVector
     10 from qiskit_aer import AerSimulator
---> 11 from qiskit.opflow import Gradient, StateFn, CircuitStateFn, Z
     12 from qiskit_machine_learning.neural_networks import OpflowQNN
     13 

ModuleNotFoundError: No module named 'qiskit.opflow'

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i expect to be able to use opflow module after installing qiskit 1.1 and the document of qiskit is not tell anything about it.

Answer 1

qiskit.opflow was deprecated sometime before qiskit 0.44. The functions and classes were migrated to other modules. Here is the list of opflow functions and where were they moved:

opflow	Alternative
qiskit.opflow.gradients	qiskit.algorithms.gradients
qiskit.opflow.state_fns.StateFn	In most cases, qiskit.quantum_info.Statevector
qiskit.opflow.state_fns.CircuitStateFn	qiskit.quantum_info.Statevector
qiskit.opflow.Z	qiskit.quantum_info.Pauli