[unitaryhack] Remove qml.utils.expand and replace with qml.operation.expand_matrix.

[maezyn]

Context:
Removes the utility function qml.utils.expand and replaces all references to it with qml.operation.expand_matrix.
Description of the Change:

• Removes qml.utils.expand and its corresponding tests.
• Replaces all references of qml.utils.expand with qml.operation.expand_matrix.
• Renames TestExpand to TestExpandVector in test_utils.py to better reflect the remaining test cases.

Benefits:
Removes the utility function qml.utils.expand which is no longer used anywhere as of #2609.
Possible Drawbacks:
Removes qml.utils.expand tests from test_utils.py.
Related GitHub Issues:
Closes #2637

[codecov]

Codecov Report

Merging #2654 (97a08af) into master (5d83fdf) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2654      +/-   ##
==========================================
- Coverage   99.61%   99.61%   -0.01%     
==========================================
  Files         251      251              
  Lines       20682    20662      -20     
==========================================
- Hits        20602    20582      -20     
  Misses         80       80              

Impacted Files	Coverage Δ
pennylane/operation.py	96.59% <ø> (ø)
pennylane/ops/qubit/parametric_ops.py	100.00% <100.00%> (ø)
pennylane/utils.py	100.00% <100.00%> (ø)

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[josh146]

thanks @mmore21 for this contribution! Is it ready for review?

[maezyn]

thanks @mmore21 for this contribution! Is it ready for review?

Hi @josh146 and @antalszava, should be ready for review. Thanks!

[antalszava]

Hi @mmore21, this is looking great, thank you for the contribution! 🙂

One thing before approval would be to extend the functionality such that qml.utils.expand is still valid, though it resolves to qml.operation.expand_matrix. Although this PR addresses all usages of qml.utils.expand, it may be that users would have their codes breaking if we made the removal in one step.

Adding the following code to the beginning of the code section of pennylane/utils.py should help:

import warnings

def __getattr__(name):
    # for more information on overwriting `__getattr__`, see https://peps.python.org/pep-0562/
    if name == "expand":
        warning_string = f"qml.utils.expand is deprecated; using qml.operation.expand_matrix instead."
        warnings.warn(warning_string, UserWarning)
        return qml.operation.expand_matrix
    try:
        return globals()[name]
    except KeyError as e:
        raise AttributeError from e

It would also be good to include a test case for this, just to make sure that a warning is raised.

Apart from this, the rest of the changes are looking great. 👍

[antalszava]

Looks good @mmore21! 🎉 Thank you so much for the contribution! 😊 Very neat 👏

[maezyn]

Thanks @antalszava, happy to make my first contribution!

[antalszava]

Hi @mmore21 great to have you contribute 🙂

As you've made your contribution during Unitary HACK you are eligible for swag. 🙂 To claim it you should be signed up for UnitaryHACK here and add [unitaryhack] in the title of the PR.

Let me know if you have further questions (cc @CatalinaAlbornoz).

[maezyn]

Awesome, just registered and updated the title. Thanks for letting me know @antalszava!

[antalszava]

Overriding the checks: coverage decrease is due to deleted lines, docs build is lagging due to concurrency issues.