qiskit.circuit.QuantumCircuit.assign_parameters¶

QuantumCircuit.assign_parameters(parameters, inplace=False, param_dict=None)[source]¶

Assign parameters to new parameters or values.

The keys of the parameter dictionary must be Parameter instances in the current circuit. The values of the dictionary can either be numeric values or new parameter objects. The values can be assigned to the current circuit object or to a copy of it.

Parameters

parameters (dict or iterable) – Either a dictionary or iterable specifying the new parameter values. If a dict, it specifies the mapping from current_parameter to new_parameter, where new_parameter can be a new parameter object or a numeric value. If an iterable, the elements are assigned to the existing parameters in the order they were inserted. You can call QuantumCircuit.parameters to check this order.
inplace (bool) – If False, a copy of the circuit with the bound parameters is returned. If True the circuit instance itself is modified.
param_dict (dict) – Deprecated, use parameters instead.

Raises

CircuitError – If parameters is a dict and contains parameters not present in the circuit.
ValueError – If parameters is a list/array and the length mismatches the number of free parameters in the circuit.

Returns

A copy of the circuit with bound parameters, if inplace is False, otherwise None.

Return type

Optional(QuantumCircuit)

Examples

Create a parameterized circuit and assign the parameters in-place.

from qiskit.circuit import QuantumCircuit, Parameter

circuit = QuantumCircuit(2)
params = [Parameter('A'), Parameter('B'), Parameter('C')]
circuit.ry(params[0], 0)
circuit.crx(params[1], 0, 1)

print('Original circuit:')
print(circuit.draw())

circuit.assign_parameters({params[0]: params[2]}, inplace=True)

print('Assigned in-place:')
print(circuit.draw())

Original circuit:

     ┌───────┐         
q_0: ┤ Ry(A) ├────■────
     └───────┘┌───┴───┐
q_1: ─────────┤ Rx(B) ├
              └───────┘
Assigned in-place:
     ┌───────┐         
q_0: ┤ Ry(C) ├────■────
     └───────┘┌───┴───┐
q_1: ─────────┤ Rx(B) ├
              └───────┘

Bind the values out-of-place and get a copy of the original circuit.

from qiskit.circuit import QuantumCircuit, ParameterVector

circuit = QuantumCircuit(2)
params = ParameterVector('P', 2)
circuit.ry(params[0], 0)
circuit.crx(params[1], 0, 1)

bound_circuit = circuit.assign_parameters({params[0]: 1, params[1]: 2})
print('Bound circuit:')
print(bound_circuit.draw())

print('The original circuit is unchanged:')
print(circuit.draw())

Bound circuit:
     ┌───────┐         
q_0: ┤ Ry(1) ├────■────
     └───────┘┌───┴───┐
q_1: ─────────┤ Rx(2) ├
              └───────┘
The original circuit is unchanged:
     ┌──────────┐            
q_0: ┤ Ry(P[0]) ├─────■──────
     └──────────┘┌────┴─────┐
q_1: ────────────┤ Rx(P[1]) ├
                 └──────────┘