Setting qutip-qip as an optional plugin for qutip-5 [unitaryhack]

[HGSilveri]

Description

• Allow imports of qutip.qip seamlessly as imports of qutip_qip
• Test the import behaviour when qutip_qip is installed and when not.

Related issues or PRs
Incorporates the ideas in the discussion of #1500.
Fixes #1893.

Todos and questions

• Have qutip-qip be an optional dependency (will be left for a future PR)
• Add installation of qutip-qip to the CI workflow

I have a draft of these changes locally, but they fail due to a dependency conflict: qutip_qip currently requires qutip<5 and >=4.6 while these changes are being implemented in v5.0.0.dev, ie >5. This will cause the unit test where qutip_qip is installed to be skipped. Any ideas on how to get around this?

Edit: Uses a stub for the qutip_qip package in the units tests instead, which removes the need of having qutip-qip installed.

Changelog

Allow imports of qutip.qip seamlessly as imports of qutip_qip.
Have qutip-qip be an optional dependency.

[BoxiLi]

Ah yes, that constraint was there to prevent accidentally using qutip-qip with qutip@dev.major because the support was only added a few weeks ago. Only the master branch of qutip-qip support this. So this basically prevents installing the qutip@dev.major and the released qutip-qip at the same time. One has to install qutip-qip@master to test them.

This also means that adding qutip-qip as an optional package right now does not make much sense. Probably we can drop this.

To test it on GitHub action we need to install qutip-qip@master for now and test the importation. @hodgestar Is that ok? Otherwise, I can try to get out a new release of qutip-qip in a day or so. Just to update the change log and click the button.

[HGSilveri]

This also means that adding qutip-qip as an optional package right now does not make much sense. Probably we can drop this.

To test it on GitHub action we need to install qutip-qip@master for now and test the importation. @hodgestar Is that ok? Otherwise, I can try to get out a new release of qutip-qip in a day or so. Just to update the change log and click the button.

Completely up to you, of course! If you choose to drop the optional dependency for now, I can also just put those changes on another PR to be merged when the time is right.
I'll stand by for your decision regarding the CI tests.

[coveralls]

Coverage increased (+0.2%) to 65.507% when pulling 2049dfd on HGSilveri:qip-module into 9bb7c7a on qutip:dev.major.

[hodgestar]

I made some suggestions to make it possible to always run the tests.

[hodgestar]

Regarding the suggestions in the TODO list:

Have qutip-qip be an optional dependency

I'm wondering about this. Having pip install qutip[qip] is nice, but what should happen with pip install qutip[full]? Should that also install qutip_qip? If not should we then leave qutip_qip out of full? And should we have qutip[full-family]?

Add installation of qutip-qip to the CI workflow

This we should not do -- we don't want anything in core qutip to accidentally require qutip_qip (that was sort of the point of the family packages).

[BoxiLi]

I'm wondering about this. Having pip install qutip[qip] is nice, but what should happen with pip install qutip[full]? Should that also install qutip_qip? If not should we then leave qutip_qip out of full? And should we have qutip[full-family]?

I understand [full] as "installing everything that might be needed so that I can run everything without any ImportError". So this means that it includes [qip]. However, I do get your concern that this will probably make the option [full] larger and larger in the future.

Nonetheless, since there is not yet a released qutip-qip that supports qutip-5. Let's leave it to a different PR.

[HGSilveri]

This we should not do -- we don't want anything in core qutip to accidentally require qutip_qip (that was sort of the point of the family packages).

Sure, no need for that anymore, I'll edit the description.

[hodgestar]

I understand [full] as "installing everything that might be needed so that I can run everything without any ImportError". So this means that it includes [qip]. However, I do get your concern that this will probably make the option [full] larger and larger in the future.

Perhaps installing qutip_qip as part of full is a good first step. It means that QuTiP 5 will just "work" as it did before and we can always remove it from full in QuTiP 5.1 or later.

[hodgestar]

I had a few more ideas about how to test this nicely.

[hodgestar]

Looks good!

[hodgestar]

@BoxiLi I'd like you to approve to since this is a very important link to qutip_qip.

Once we have Boxi's approval and the tests pass, I think we can consider this done.

[BoxiLi]

Looks great! Also tested it locally with/without an installed qutip-qip.