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list-reverse-copy (FURB187)

Added in 0.5.0 · Related issues · View source

Derived from the refurb linter.

Fix is always available.

What it does

Checks for list reversals that can be performed in-place in lieu of creating a new list.

Why is this bad?

When reversing a list, it's more efficient to use the in-place method .reverse() instead of creating a new list, if the original list is no longer needed.

Example

l = [1, 2, 3]
l = reversed(l)

l = [1, 2, 3]
l = list(reversed(l))

l = [1, 2, 3]
l = l[::-1]

Use instead:

l = [1, 2, 3]
l.reverse()

Fix safety

This rule's fix is marked as unsafe, as calling .reverse() on a list will mutate the list in-place, unlike reversed, which creates a new list and leaves the original list unchanged.

If the list is referenced elsewhere, this could lead to unexpected behavior.

References