Gates do not check if complex inputs passed in

[nonhermitian]

Information

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

What is the current behavior?

This works:

from qiskit import *

qc = QuantumCircuit(2, 2)
qc.h(0)
qc.rx(1+1j, 0)
qc.cx(0, 1)
qc.measure([0, 1], [0, 1])

qc.draw()

but it should not. It only gets caught later with:

TypeError: can't convert complex to float

Steps to reproduce the problem

What is the expected behavior?

Suggested solutions

[1ucian0]

We support several types as parameters (symbolic, numpy types, ...). Making type checking at gate construction time might be expensive. Do we want to go that way?

[nonhermitian]

@1ucian0 Not sure why checking for the validity of inputs is "low priority" in your mind? Also, we do a fair bit of type checking already for parameters, just not in the sanity checking sense:

https://github.com/Qiskit/qiskit-terra/blob/89cb7afc68b02850565f04851f1c17359afcf52c/qiskit/circuit/instruction.py#L137

[1ucian0]

Reopening, since #3668 was reverted in #4117