39 – Automatic enumeration values

39 – Automatic enumeration values#

The module enum provides a function auto that you can use to automatically generate values for your enumeration members.

The default behaviour is to create successive integers starting at 1 for a standard enumeration:

from enum import Enum, auto

class Letter(Enum):
    A = auto()
    B = auto()

print(Letter.A.value)  # 1
print(Letter.B.value)  # 2

The function auto is also smart enough to specialise appropriately, depending on the type of enumeration.

For flag enumerations, it produces powers of 2 for the flags:

from enum import Flag, auto

class Permissions(Flag):
    READ = auto()     # 1
    WRITE = auto()    # 2
    EXECUTE = auto()  # 4

print(repr(Permissions.EXECUTE))
# <Permissions.EXECUTE: 4>

For string enumerations, it generates lowercase strings that match the member names:

from enum import StrEnum, auto

class Direction(StrEnum):
    NORTH = auto()  # north
    SOUTH = auto()  # south
    ...

print(repr(Direction.NORTH))
# <Direction.NORTH: 'north'>