manual-list-copy (PERF402)

Derived from the Perflint linter.

What it does

Checks for for loops that can be replaced by a making a copy of a list.

Why is this bad?

When creating a copy of an existing list using a for-loop, prefer list or list.copy instead. Making a direct copy is more readable and more performant.

Using the below as an example, the list-based copy is ~2x faster on Python 3.11.

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:
    filtered.append(i)

Use instead:

original = list(range(10000))
filtered = list(original)