Fix #324: use match for better readability and typing

[thierry-martinez]

This commit replaces if/elif/else chains with match when the conditions perform equality comparisons on the same subject. These changes improve readibility and avoid mypy shortcomings related to type narrowing.

Before this commit, PLR1714 suggested rewriting code such as:

if cmd.kind == CommandKind.X or cmd.kind == CommandKind.Z: ...

into:

if cmd.kind in {CommandKind.X, CommandKind.Z}: ...

However, mypy does not currently infer that cmd is an instance of X or Z within the if block when set membership is used.

With this commit, the condition is expressed using an or-pattern, and type checking behaves as expected:

match cmd.kind:
    case CommandKind.X | CommandKind.Z: ...

[codecov]

Codecov Report

❌ Patch coverage is 76.97994% with 218 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.98%. Comparing base (03a89c9) to head (1d08801).

Files with missing lines	Patch %	Lines
graphix/flow/exceptions.py	0.00%	68 Missing ⚠️
graphix/pattern.py	74.87%	51 Missing ⚠️
graphix/sim/tensornet.py	52.00%	24 Missing ⚠️
graphix/optimization.py	77.89%	21 Missing ⚠️
graphix/transpiler.py	93.06%	12 Missing ⚠️
graphix/qasm3_exporter.py	86.95%	9 Missing ⚠️
graphix/simulator.py	77.41%	7 Missing ⚠️
graphix/pretty_print.py	92.85%	6 Missing ⚠️
graphix/fundamentals.py	87.50%	5 Missing ⚠️
graphix/graphsim.py	73.68%	5 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
- Coverage   88.76%   87.98%   -0.78%     
==========================================
  Files          44       44              
  Lines        6308     6443     +135     
==========================================
+ Hits         5599     5669      +70     
- Misses        709      774      +65     

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[emlynsg]

I've suggested additional places to replace if else with match. Happy to discuss.
I also found a few other locations:

• ops.py from L221
• pauli.py from L71 (eigenstate and _repr_impl and _matmul_impl functions).

[emlynsg]

Minor but slight readability improvement:

match instr.axis:
    case Axis.X:
        circuit.h(instr.target)
        circuit.m(instr.target, Axis.Z)
    case Axis.Y:
        circuit.rx(instr.target, ANGLE_PI / 2)
        circuit.m(instr.target, Axis.Z)
    case _:
        circuit.add(instr)

Could possibly do the same to the outer if else.

[emlynsg]

Similar here:

match cmd.plane:
    case Plane.XY:
        gate = "rx"
        angle = -cmd.angle
    case Plane.XZ:
        gate = "ry"
        angle = -cmd.angle
    case Plane.YZ:
        gate = "rx"
        angle = cmd.angle
    case _:
        assert_never(cmd.plane)

[emlynsg]

Can change to match here

[emlynsg]

Can replace these with match too

[emlynsg]

Replace with match.

[thierry-martinez]

Thank you, @emlynsg, for spotting these missing cases. I updated the refactoring script, and the rewriting should now be more systematic: https://github.com/thierry-martinez/graphix-refactoring/blob/main/src/if_to_match.py

The main change was to treat sequences of if ...: return statements as if/elif chains.

Note that I needed to fix typing issues now that the new numba==0.64.0 is compatible with numpy==2.4. I added numba and numpy to the list of packages with pinned versions to prevent these kinds of errors from being mixed up with other PRs in the future.

[emlynsg]

Looks great to me. Would be interested in you explaining the refactoring tool at some point!