11.1. OOP Enum

11.1.1. Rationale

  • List of finite choices

  • Enumerations

  • Enum

  • IntEnum

  • Flag

  • IntFlag

11.1.2. Definition

Defining enum:

from enum import Enum


class Color(Enum):
    RED = '#00FF00'
    GREEN = '#00FF00'
    BLUE = '#0000FF'


color = Color.RED

Defining enum:

from enum import Enum

class Status(Enum):
    ALIVE = 'alive'
    DEAD = 'dead'

11.1.3. Accessing names and values

Accessing names and values:

from enum import Enum

class Color(Enum):
    RED = '#FF0000'
    GREEN = '#00FF00'
    BLUE = '#0000FF'


print(Color.RED)        # Color.RED
print(Color.RED.name)   # RED
print(Color.RED.value)  # '#FF0000'

from enum import Enum


class Status(Enum):
    FULL_HEALTH = 100
    DEAD = 0


hit_points = 100
status = Status(hit_points)
print(status)
# Status.FULL_HEALTH


hit_points = 0
status = Status(hit_points)
print(status)
# Status.DEAD

11.1.4. Iterating over Enum

Iterating over Enum:

from enum import Enum

class Color(Enum):
    RED = '#00FF00'
    GREEN = '#00FF00'
    BLUE = '#0000FF'

for color in Color:
    print(color)

# Color.RED
# Color.GREEN
# Color.BLUE

11.1.5. Identity check

Identity check:

color = Color('#00FF00')     # <Color.GREEN: '#00FF00'>
color is Color.RED           # False
color is Color.GREEN         # True

11.1.6. Use cases

enum - Example usage:

from enum import Enum

class Permission(Enum):
    READ_WRITE_EXECUTE = 0b111
    READ_WRITE = 0b110
    READ_EXECUTE = 0b101
    READ = 0b100
    WRITE_EXECUTE = 0b011
    WRITE = 0b010
    EXECUTE = 0b001
    NONE = 0b000

import os
from enum import Enum

class Permission(Enum):
    READ_WRITE_EXECUTE = 0b111
    READ_WRITE = 0b110
    READ_EXECUTE = 0b101
    READ = 0b100
    WRITE_EXECUTE = 0b011
    WRITE = 0b010
    EXECUTE = 0b001
    NONE = 0b000


os.stat('/tmp/myfile.txt')
# os.stat_result(
#   st_mode=33260,
#   st_ino=44792722,
#   st_dev=16777222,
#   st_nlink=1,
#   st_uid=501,
#   st_gid=0,
#   st_size=2930,
#   st_atime=1587481434,
#   st_mtime=1587481422,
#   st_ctime=1587484635)

permissions = os.stat('/tmp/myfile.txt').st_mode

print(f'dec={permissions}, oct={oct(permissions)}, bin={bin(permissions)}')
# dec=33260, oct=0o100754, bin=0b1000000111101100

*_, user, group, others = oct(permissions)

print(f'{user=} {group=} {others=}')
# user='7' group='5' others='4'

Permission(int(user))
# <Permission.READ_WRITE_EXECUTE: 7>

Permission(int(group))
# <Permission.READ_EXECUTE: 5>

Permission(int(others))
# <Permission.READ: 4>

enum - Example usage:

from enum import IntEnum

class IndexDrives(IntEnum):
    """ This enum holds the index value of drive object entries
    """
    ControlWord = 0x6040
    StatusWord = 0x6041
    OperationMode = 0x6060

11.1.7. Pattern Matching

  • Since Python 3.10: PEP 636 -- Structural Pattern Matching: Tutorial

request = 'GET 1.1 /index.html'

match request.split():
    case ['GET', version, uri]:
        server.get(uri)
    case ['POST', version, uri]:
        server.post(uri)
    case ['PUT', version, uri]:
        server.put(uri)
    case ['DELETE', version, uri]:
        server.delete(uri)

def http_error(status):
    match status:
        case 400:
            return 'Bad request'
        case 401 | 403 | 404:
            return 'Not allowed'
        case 404:
            return 'Not found'
        case 418:
            return "I'm a teapot"
        case _:
            return 'Unexpected status'

match hero.action():
    case ['move', ('up'|'down'|'left'|'right') as direction, value]:
        hero.move(direction, value)
    case ['make_damage', value]:
        hero.make_damage(value)
    case ['take_damage', value]:
        hero.take_damage(value)

from enum import Enum

class Key(Enum):
    ESC = 27
    ARROW_LEFT = 37
    ARROW_UP = 38
    ARROW_RIGHT = 39
    ARROW_DOWN = 40

match keyboard.on_key_press():
    case Key.ESC:
        game.quit()
    case Key.ARROW_LEFT:
        game.move_left()
    case Key.ARROW_UP:
        game.move_up()
    case Key.ARROW_RIGHT:
        game.move_right()
    case Key.ARROW_DOWN:
        game.move_down()
    case _:
        raise ValueError(f'Unrecognized key')

from enum import Enum

class Color(Enum):
    RED = 0
    BLUE = 1
    BLACK = 2

match color:
    case Color.RED:
        print('Soviet')
    case Color.BLUE:
        print('Allies')
    case Color.BLACK:
        print('Axis')

from enum import Enum

class SpaceMan(Enum):
    NASA = 'Astronaut'
    ESA = 'Astronaut'
    ROSCOSMOS = 'Cosmonaut'
    CNSA = 'Taikonaut'
    ISRO = 'GaganYatri'

match agency:
    case SpaceMan.NASA:
        print('USA')
    case SpaceMan.ESA:
        print('Europe')
    case SpaceMan.ROSCOSMOS:
        print('Russia')
    case SpaceMan.CNSA:
        print('China')
    case SpaceMan.ISRO:
        print('India')

11.1.8. Assignments

Todo

Create assignments