len-test (PLC1802)

Derived from the Pylint linter.

Fix is always available.

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

What it does

Checks for usage of call of 'len' on sequences in boolean test context.

Empty sequences are considered false in a boolean context. You can either remove the call to 'len' or compare the length against a scalar.

fruits = ["orange", "apple"]
vegetables = []

if len(fruits):
    print(fruits)

if not len(vegetables):
    print(vegetables)

Use instead:

fruits = ["orange", "apple"]

if fruits:
    print(fruits)

if not vegetables:
    print(vegetables)