Allow numbers.Integral instead of only built-in int for QuantumRegister index

[arunraja-hub]

Summary

Fixes #3929

Details and comments

-I changed line 120/121 of register.py such that it includes numbers.Integral as an allowable type for an index of a QuantumRegister. This is my first issue! Excited to contribute more
Issue: #3929

[CLAassistant]

All committers have signed the CLA.

[Cryoris]

Thanks for the contribution @arunraja-hub! Can you add a test that checks passing different types of integers as register sizes? I.e. a test that fails without your PR but works afterwards.
And could you also add a bugfix releasenote, where you're saying that not only Python int are allowed but any integer of type numbers.Integral? How add a releasenote is described here.

[arunraja-hub]

Hi @Cryoris , Thank you! Could you provide more info on implementing the test? is there any documentation on that?

[Cryoris]

Here are some comments on the contribution 🙂

[Cryoris]

I don't think there's a dedicated documentation for the tests, but essentially a test is a short snippet of code that checks your new feature works. In a bugfix test, you ideally have a snippet that didn't work before but now does. E.g. something like

def test_register_int_types(self):
    ints = [int(2), int64(2), np.int(2), np.integer(2), ... ] # all int types you can think of
    for size in ints:
        with self.subTest(size=size):  # technically not necessary, but nicer for debugging if you add this
            qr = QuantumRegister(size)
            cr = ClassicalRegister(size)
            self.assertEqual(qr.size, 2)
            self.assertEqual(cr.size, 2)

See test/python/circuit/test_circuit_registers.py for where you could implement the test and how others look like.

Let me know if you have any questions!

[arunraja-hub]

test_register_int_types passed when I ran the command make test
However, according to github's checks below there seem to be 2 cases that are failing. Why is this the case?

[Cryoris]

The CI also runs a linter and stylechecker on the code, you can do this locally by doing make lint and make style in the command line. The output is

test/python/circuit/test_circuit_registers.py:61:1: W293 blank line contains whitespace
test/python/circuit/test_circuit_registers.py:63:77: W291 trailing whitespace
test/python/circuit/test_circuit_registers.py:65:44: E202 whitespace before ']'
test/python/circuit/test_circuit_registers.py:65:46: W291 trailing whitespace
test/python/circuit/test_circuit_registers.py:67:42: W291 trailing whitespace

If you fix this, the tests will passs.

[arunraja-hub]

@Cryoris Completed the tests for int32 and int64. I believe this PR is all set
Do I need to do anything else?

[Cryoris]

Actually I misunderstood the goal, I though the size should accept all types not the index. The tests should be changed accordingly to check that all these integer types work as indices of QuantumRegister and ClassicalRegister. You could e.g. change the test to do something like

for index in [np.int(2), np.int32(2), ... ]:
        # ... sub test as before, and the same for classical register
        qr = QuantumRegister(3)
        self.assertEqual(qr[index], qr[2])

[arunraja-hub]

Ths issue was that I had a newline. So I removed. Now the lint error is that I have removed a newline. So it is contradictory
https://dev.azure.com/qiskit-ci/qiskit-terra/_build/results?buildId=16523&view=logs&j=7684b0c9-af38-5400-184f-6880bd8a4dd7&t=9d95188b-4e59-58d8-f7c4-3f1fbd4209ad&l=12

[arunraja-hub]

Hi @Cryoris, May I confirm that this PR is complete? Also, could you assign this issue to me? Thank you

[Cryoris]

Yes, it is! Thanks a lot for the contribution 🚀

[arunraja-hub]

Thank you @Cryoris
Are there other issues I can work on next?