Inefficient membership test (ARCH2075)

Key python.performance.inefficient-membership-test · Severity info · Category performance

An in check against a list is O(n) and slow when repeated, especially inside a loop. Convert the searched collection to a set for O(1) lookups.

Incorrect

def filter_allowed(items):
    allowed = ["read", "write", "admin", "audit"]
    return [i for i in items if i.role in allowed]

Correct

def filter_allowed(items):
    allowed = {"read", "write", "admin", "audit"}
    return [i for i in items if i.role in allowed]

Fix

Define the repeatedly-tested collection as a set instead of a list.