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for-loop-set-mutations (FURB142)

Preview (since v0.3.5) · Related issues · View source

Derived from the refurb linter.

Fix is always available.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for code that updates a set with the contents of an iterable by using a for loop to call .add() or .discard() on each element separately.

Why is this bad?

When adding or removing a batch of elements to or from a set, it's more idiomatic to use a single method call rather than adding or removing elements one by one.

Example

s = set()

for x in (1, 2, 3):
    s.add(x)

for x in (1, 2, 3):
    s.discard(x)

Use instead:

s = set()

s.update((1, 2, 3))
s.difference_update((1, 2, 3))

Fix safety

The fix will be marked as unsafe if applying the fix would delete any comments. Otherwise, it is marked as safe.

References