Lint

[oliver-sanders]

Small lint fixes for rules not currently covered by our CI, low priority.

Took ruff for a spin to see how handy its code fixers are (it's not just a linter, it can fix some issues for you). Some of the fixers are kinda useful, but most the good rules have to be done manually, so turns out they aren't that helpful for us, worth a try, never mind.

Kept a four of the fixes and turned them into this PR. They're mostly small, but B904 created a good bit of diff. Long story short, if you're re-raising an exception with a more helpful class/message, you generally want to do raise Exception(...) from None, otherwise the context of the exception you're re-raising is included in the traceback which kinda defates the object.

I.E:

from cylc.flow.exceptions import InputError

try:
    # the general exception we are catching
    raise Exception('foo')
except Exception as exc:
    # the specific exception we are raising
    raise InputError('bar')

Preserves the parent exception context resulting in a confusing traceback:

Traceback (most recent call last):
  File "/var/tmp/tmp.wlysihZu3M/mess.py", line 5, in <module>
    raise Exception('foo')
Exception: foo

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/tmp/tmp.wlysihZu3M/mess.py", line 8, in <module>
    raise InputError('bar')
cylc.flow.exceptions.InputError: bar

Whereas:

from cylc.flow.exceptions import InputError

try:
    # the general exception we are catching
    raise Exception('foo')
except Exception as exc:
    # the specific exception we are raising
    raise InputError('bar') from None

Chops off the parent context:

Traceback (most recent call last):
  File "/var/tmp/tmp.wlysihZu3M/mess.py", line 8, in <module>
    raise InputError('bar') from None
cylc.flow.exceptions.InputError: bar

Using from exc is the same as the default behaviour (just more explicit).

Raising the whole exception tree is a useful feature for debugging uncaught errors, but not so good for errors we are trying to niceify for users.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• CHANGES.md entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

RUF015: Get the first item from the iterator rather than working through the whole iterator, turning it into a list, then getting the first item.

[oliver-sanders]

B904: Don't include the ContactFileExists exception context in the ServiceFileError.

[oliver-sanders]

PERF101: don't needless iterate items

[oliver-sanders]

PERF402: Don't build an entire list when you only need one item

[hjoliver]

Nice, worth doing!