Add a parameters method to the operators

[Cryoris]

What is the expected behavior?

Calling QuantumCircuit.parameters returns a set of the Parameter objects in the circuit.
The OperatorBase should support this too, since it too can be parameterized.

[techwithshadab]

Hi @Cryoris
Can you point me to the QuantumCircuit.parameters file?

[Cryoris]

It's a method here: https://github.com/Qiskit/qiskit-terra/blob/76f21b011171486ccc77775ea29f51be196755e2/qiskit/circuit/quantumcircuit.py#L1645

In an OperatorBase either the coefficients can be parameterized (ie of type ParameterExpression -- careful, this is not the same as a plain Parameter) or if it contains a CircuitOp or CircuitStateFn, the underlying circuit can be parameterized. You can probably recursively check these two and return a set of all Parameters you found,.

[VANRao-Stack]

It's a method here: https://github.com/Qiskit/qiskit-terra/blob/76f21b011171486ccc77775ea29f51be196755e2/qiskit/circuit/quantumcircuit.py#L1645
In an OperatorBase either the coefficients can be parameterized (ie of type ParameterExpression -- careful, this is not the same as a plain Parameter) or if it contains a CircuitOp or CircuitStateFn, the underlying circuit can be parameterized. You can probably recursively check these two and return a set of all Parameters you found,.

I see that the OperatorBase class can accept coefficients of different types like int, float etc. Is the code expected to return all those coefficients for this feature request? Also, if it does contain the ParamterExpression, is it supposed to return the ParamterExpression object?

[Cryoris]

It's supposed to only return the Parameter objects, no floats/ints. If you have a ParameterExpression you can get the Parameters it contains by ParameterExpression.parameters. Essentially the behaviour should be the same as for the QuantumCircuit and its parameters method 🙂

[woodsp-ibm]

Closed as solved by #1194