Skip to content

unnecessary-list-cast (PERF101)#

Derived from the Perflint linter.

Fix is always available.

What it does#

Checks for explicit casts to list on for-loop iterables.

Why is this bad?#

Using a list() call to eagerly iterate over an already-iterable type (like a tuple, list, or set) is inefficient, as it forces Python to create a new list unnecessarily.

Removing the list() call will not change the behavior of the code, but may improve performance.

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.


items = (1, 2, 3)
for i in list(items):

Use instead:

items = (1, 2, 3)
for i in items: