Question

What first pops into my head is a dictionary with keys acting as list values and dictionary values defaulting to None, but this feels sub-optimal to me. Can anyone propose a single-structure (i.e. no separate ‘options’ dict) alternative where dict[key] on an item with no flags set returns None and otherwise returns a list of flags? Apologies if I am overlooking some obvious convention.

A simple use for this structure could be an order instance where each item can optionally contain modifications (i.e. no nuts).

Answer 1

Maybe a defaultdict will do:

from collections import defaultdict

flags = defaultdict(lambda : None)
flags.update({'F1':True,'F3':True,'F8':True})

for f in 'F1 F2 F3 F4 F5 F6 F7 F8'.split():
    print f, '->', flags[f]

Prints:

F1 -> True
F2 -> None
F3 -> True
F4 -> None
F5 -> None
F6 -> None
F7 -> None
F8 -> True