• Ruff version: 0.3.3
• Linter rule: unnecessary-lambda / PLW0108

Example

def foo(a, b):
  return a + b

def bar(c, d):
  return c, d

HANDLERS = {
  "foo": foo,
  "bar": lambda a, b: bar(a, b)  # "fixes" to just bar 
}

def handle(verb: str, payload):
  a, b = payload
  return HANDLERS[verb](a=a, b=b)

Here we're relying on the lambda to implement renaming of positional arguments. Removing the lambda expression would be incorrect despite an absence of side-effects. A correct refactor would be to rename the arguments to bar, or to eliminate the keyword invocation but the linter fix alone is unsafe despite listing itself as such.