Parameter is_real seems not correct

[ikkoham]

Environment

• Qiskit Terra version:
• Python version:
• Operating system:

What is happening?

Parameter.is_real() seems not correct.

How can we reproduce the issue?

>>> from qiskit.circuit import Parameter

>>> Parameter("a").is_real()
True
>>> (1j * Parameter("a")).is_real()
True

What should happen?

Both should return False since we don't know whether a is real or not.

Any suggestions?

No response

[jlapeyre]

Didn't we already discuss whether to use three-level logic here ? @Cryoris

[Cryoris]

Yeah, we did 🙂 The plan was to do the same as sympy and symengine: return None while the expression is not bound, otherwise True or False accordingly