Refactor measure operator in a new pauli module

[thierry-martinez]

This pull-request introduces a pauli module for symbolic Pauli calculations, which are used in statevec instead of direct matrix computation. The test_pauli module checks that the computations are the same as before, modulo a bug fix: CLIFFORD[CLIFFORD_CONJ[vop]] was used instead of CLIFFORD[vop].conj().T, despite the two are only equal modulo phase in the general case (see the comment in pauli.py). The new implementation allows the angle and the plane to be computed separately from the state vector back-end, which will be useful for future client/server computations and to share the code with other back-ends.

[thierry-martinez]

Do we still want to support Python <3.10, or may we bump version constraint to allow match construct?

[shinich1]

Do we still want to support Python <3.10, or may we bump version constraint to allow match construct?

Good point, we might ditch 3.8 soon-ish but not sure yet about 3.9. Are there significant differences? if we can work around with a few lines of additional code, my personal opinion is it's good to keep supporting 3.9. What's your thoughts?

[thierry-martinez]

Are there significant differences? if we can work around with a few lines of additional code, my personal opinion is it's good to keep supporting 3.9. What's your thoughts?

Python 3.10 introduced match-blocks, allowing branching code to be written more elegantly by pattern-matching instead of if-elif-else chains. I rewrote in d7f7683 the few match-blocks I introduced into if-elif-else chains to be compatible with Python <3.10.

Python 3.9 allowed list and tuple types to be written as list[...] and tuple[...] instead of typing.List[...] and typing.Tuple[...]. I rewrote the types in 386f718 to be compatible with Python <3.9.

I think that when we will be ready to move to Python 3.10, match-blocks will allow many code places to be written in a more readable way, but there is no urgency to do so.

[shinich1]

Are there significant differences? if we can work around with a few lines of additional code, my personal opinion is it's good to keep supporting 3.9. What's your thoughts?

Python 3.10 introduced match-blocks, allowing branching code to be written more elegantly by pattern-matching instead of if-elif-else chains. I rewrote in d7f7683 the few match-blocks I introduced into if-elif-else chains to be compatible with Python <3.10.

Python 3.9 allowed list and tuple types to be written as list[...] and tuple[...] instead of typing.List[...] and typing.Tuple[...]. I rewrote the types in 386f718 to be compatible with Python <3.9.

I think that when we will be ready to move to Python 3.10, match-blocks will allow many code places to be written in a more readable way, but there is no urgency to do so.

Thanks, that seems pretty good, let me think a bit. @masa10-f: let's discuss this next week.

[thierry-martinez]

Thanks! Merged.