Micro-optimizations

[cclauss]

Ruff rules:

• C408 Unnecessary tuple call (rewrite as a literal)
• PERF401 Use a list comprehension to create a transformed list
• PLR1714 Consider merging multiple comparisons. Use a set if the elements are hashable.
• RET503 Missing explicit return at the end of function able to return non-None value
• RUF015 Prefer next(iter(channel_layer.channels)) over single element slice
• SIM210 Use bool(...) instead of True if ... else False

% ruff rule PERF401

manual-list-comprehension (PERF401)

Derived from the Perflint linter.

What it does

Checks for for loops that can be replaced by a list comprehension.

Why is this bad?

When creating a transformed list from an existing list using a for-loop, prefer a list comprehension. List comprehensions are more readable and more performant.

Using the below as an example, the list comprehension is ~10% faster on Python 3.11, and ~25% faster on Python 3.10.

Note that, as with all perflint rules, this is only intended as a micro-optimization, and will have a negligible impact on performance in most cases.

Example

original = list(range(10000))
filtered = []
for i in original:
    if i % 2:
        filtered.append(i)

Use instead:

original = list(range(10000))
filtered = [x for x in original if x % 2]

If you're appending to an existing list, use the extend method instead:

original = list(range(10000))
filtered.extend(x for x in original if x % 2)