Thanks Max - I think this might be specific to string inputs? They got added after strict, iirc.

I think this might be specific to string inputs? They got added after strict, iirc.

Yes, you are right. Using a Parameter object works as expected.

from qiskit.circuit import Parameter, QuantumCircuit

qc = QuantumCircuit(2)
a = Parameter("a")
print("Testing assignment by parameter")
qc.assign_parameters({a: 1.0}, strict=False)
print("Testing assignment by string")
qc.assign_parameters({"a": 1.0}, strict=False)

Outputs:

Testing assignment by parameter
Testing assignment by string
Traceback (most recent call last):
  File "/home/oss/Files/Dev/Qiskit/qiskit/main/tmp-assign-strict.py", line 8, in <module>
    qc.assign_parameters({"a": 1.0}, strict=False)
  File "/home/oss/Files/Dev/Qiskit/qiskit/main/qiskit/circuit/quantumcircuit.py", line 4267, in assign_parameters
    raw_mapping = parameters if flat_input else self._unroll_param_dict(parameters)
                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/oss/Files/Dev/Qiskit/qiskit/main/qiskit/circuit/quantumcircuit.py", line 4357, in _unroll_param_dict
    out[self.get_parameter(parameter)] = value
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/oss/Files/Dev/Qiskit/qiskit/main/qiskit/circuit/quantumcircuit.py", line 2609, in get_parameter
    raise KeyError(f"no parameter named '{name}' is present")
KeyError: "no parameter named 'a' is present"

I.e. only the last line of the code (with the string-based parameter assignment) fails

hi @jakelishman
Can you please assign this issue to me? I would be happy to close this issue.
Thanks

Hi @jakelishman
I would be happy to take this, if its not been solved already.

Thanks Kalyan - I'll assign you, and we'll start getting the permissions set up to make you a member of the Qiskit organisation.

@Raghav-Bell: sorry, I'd not seen that message before, and now I need to assign the issue internally. Sorry for the lack of response.

@jakelishman do you expect the argument to be ignored when strict = False, irrespective of whether it is a Parameter type or a string type? A string input is an error anyway right.

Kalyan: strings are acceptable arguments; they're looked up with get_parameter. Normally we just raise the error if there's no parameter of the corresponding name, but if strict=False we shouldn't raise an error, and ignore it instead. Actually incorrect types (like an int or something weird) can just continue to throw whatever exception they eventually do, even in strict=False.