He's using the incorrect datatype for ap_list. This is apprently the collection of AP's already seen, and used with this pattern: ap_list = [] if AP not in

He's using the incorrect datatype for ap_list. This is apprently the collection of AP's already seen, and used with this pattern: ap_list = [] if AP not in ap_list: ap_list.append(AP) print AP It works, but does a linear scan every time. It's better to use a set() in such a case: ap_seen = set() if AP not in ap_seen: ap_seen.add(AP) print AP For looking up things, a set (essentially a dict without values) is much quicker than a list. Is this premature optimisation? Perhaps, but using a list for this purpose is also a code smell.