Log messages emitted on imports

[SquidDev]

Informations

• Qiskit Aer version:
• Python version: Python 3.8.10
• Operating system: Linux (Ubuntu 22.04.1 LTS)

What is the current behavior?

Importing any qiskit.aer module will log several messages of the form:

INFO:qiskit.compiler.assembler:Total Assembly Time - 0.13256 (ms)

Steps to reproduce the problem

Run the following Python program:

import logging
logging.basicConfig(level="DEBUG")
import qiskit.providers.aer

What is the expected behavior?

Importing a module ideally would not log any messages.

Suggested solutions

The easiest option here would be to change the backend detection code to run when the list of backends is requested, rather when in the constructor - happy to put a PR together for that.

There was an alternative solution proposed in Qiskit/qiskit#7498 (comment) which suggested (if I understand correctly) removing the assembling of circuits in available_methods/available_devices and replacing it with some metadata on the binary.

[hhorii]

Instead of calling cpp_execute_qobj, calling cpp_execute_circuits will resolve this issue once #1717 is merged.

available_methods is constant for a binary. However, available_devices depends on environment: ["CPU"] or ["CPU", "GPU", "Thrust"]. But just for checking availability of GPU, calling CPU and GPU may be not-small overheads.