How to use bitwise flags in Python

Question

from enum import Enum

class InputTypes(Enum):
    """
    Flags to represent the different kinds of input we
    are acting on from the user
    """
    KEYBOARD = 0b00000001,
    MOUSE_BUTTONS = 0b00000010,
    MOUSE_MOVE = 0b00000100,
    ALL = 0b11111111


if __name__ == "__main__":
    x = (InputTypes.KEYBOARD | InputTypes.MOUSE_BUTTONS)

I am getting an error:

TypeError: unsupported operand type(s) for |: 'InputTypes' and 'InputTypes'

How do I properly define some flags and use them, in python 2.7 and in python3?

Asked By: Christopher Pisz

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Source

Answer 1

Instead of using the basic Enum, you could use an IntFlag:

from enum import IntFlag
class InputTypes(IntFlag):
    # Rest of your code

Answered By: Mureinik

Answer 2

The Enum base class overrides class variable access to make them return an instance of the subclass itself. If you don’t subclass Enum (and remove the commas), your code will not crash.

Note that you can use sets of Enum entries instead of bit maps to obtain the same result using InputTypes(Enum)

Answered By: Alain T.

Answer 3

For Python 2 you want to use aenum (Advanced Enum)¹. If the numeric values are not important you can use Flag:

from aenum import Flag, auto

class InputTypes(Flag):
    """
    Flags to represent the different kinds of input we
    are acting on from the user
    """
    KEYBOARD = auto()
    MOUSE_BUTTONS = auto()
    MOUSE_MOVE = auto()
    ALL = KEYBOARD | MOUSE_BUTTONS | MOUSE_MOVE

If the values are important (meaning you’ll be using them as integers), then use IntFlag instead.

¹ Disclosure: I am the author of the Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) library.

Answered By: Ethan Furman

How to use bitwise flags in Python

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