Bound ParameterExpressions do not match the hash of an equal object of a numeric type

[wshanks]

Environment

• Qiskit version: 1.1.0
• Python version: 3.11
• Operating system: Fedora Linux 40

What is happening?

When all the parameters in a ParameterExpression are bound, it becomes equal to a float, int, or complex. However, it still uses its own hashing algorithm, so it does not hash to the same value as the numeric type. The Python data model documents that objects that compare equal should hash to the same value.

How can we reproduce the issue?

from qiskit.circuit import Parameter


a = Parameter("a")
b = a.bind({a: 1.2})
b == 1.2  # True
hash(b)  == hash(1.2)  # False

What should happen?

As much as possible, the Python data model should be followed. At some points in the parameter handling code, bound ParameterExpressions are eagerly cast to float. For example, the float(p) here:

qiskit/qiskit/transpiler/passes/scheduling/scheduling/base_scheduler.py

Line 71 in 26886a1

cal_key = tuple(indices), tuple(float(p) for p in node.op.params)

I think this is done to avoid a bound p failing the lookup if the calibrations dict was keyed with a plain float. It would be preferable not to have to deal with type casting in these cases.

Any suggestions?

No response