134 – Invertible flags

The special values True and False are tightly connected: they mean the opposite of each other and you can negate one to get the other:

• not True gives False

• not False gives True

You can create the same behaviour and the same semantics of “two opposite values” by using a flag enumeration with only two members with values 0 and 1:

from enum import Flag

class DoorState(Flag):
    CLOSED = 0
    OPEN = 1

print(~DoorState.CLOSED)  # DoorState.OPEN
print(~DoorState.OPEN)    # DoorState.CLOSED

The bitwise operator ~ (NOT) negates the flag, turning it into the opposite member.

You can also use the keyword not to do the negation, but in that case you need to reinstantiate the flag to make it a member of the enumeration again:

print(DoorState(not DoorState.CLOSED))
# DoorState.OPEN
print(DoorState(not DoorState.OPEN))
# DoorState.CLOSED

Useful for user configurations where you want readable options!