Qiskit-terra: QuantumCircuit constructor fails if n_qubits is np.int64

[kdk]

What is the expected enhancement?

Python 3.5.6 |Anaconda, Inc.| (default, Aug 26 2018, 16:30:03)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> import qiskit as qk
>>> n = np.int64(12)
>>> qr = qk.QuantumRegister(n)
>>> qc = qk.QuantumCircuit(n)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/circuit/quantumcircuit.py", line 157, in __init__
    self.add_register(*regs)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/circuit/quantumcircuit.py", line 541, in add_register
    if register.name in [reg.name for reg in self.qregs + self.cregs]:
AttributeError: 'numpy.int64' object has no attribute 'name'

Similar to as was added for Registers in #2288, the QuantumCircuit constructor should test if a provided argument can be cast to an int before it raises an error.

For reference, here is where Register does the check:
https://github.com/Qiskit/qiskit-terra/blob/2ee7a3a/qiskit/circuit/register.py#L39

and where QuantumCircuit makes new Registers from the provided int:
https://github.com/Qiskit/qiskit-terra/blob/703c9a3/qiskit/circuit/quantumcircuit.py#L522

[javabster]

@1ucian0 have you made progress on this? I'd like to give it a go if not (I'm new to qiskit and open source and this looks like a nice first issue to try out!)

[1ucian0]

Sure! Go ahead!

[javabster]

Yay great I'll get cracking! Is there a corresponding test file that needs updating as well?

[1ucian0]

Yes, tests should be added (maybe in the files we already have?). You can use the code from OP for that.