10.1. OOP Enum

10.1.1. Rationale

  • List of finite choices

  • Enumerations

  • Enum

  • IntEnum

  • Flag

  • IntFlag

10.1.2. Example

>>> from enum import Enum
>>>
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'
>>> from enum import Enum
>>>
>>>
>>> class HTTPStatus(Enum):
...     OK = 200
...     CREATED = 201
...     BAD_REQUEST = 400
...     NOT_FOUND = 404
...     INTERNAL_ERROR = 500
>>> from enum import Enum
>>>
>>>
>>> class Status(Enum):
...     ALIVE = 'alive'
...     DEAD = 'dead'

10.1.3. Switch

>>> from enum import Enum
>>>
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'
>>>
>>>
>>> mycolor = Color('#00FF00')
>>>
>>> mycolor
<Color.GREEN: '#00FF00'>
>>>
>>> mycolor.name
'GREEN'
>>>
>>> mycolor.value
'#00FF00'

10.1.4. Identity Check

>>> from enum import Enum
>>>
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'
>>>
>>>
>>> mycolor = Color('#00FF00')
>>>
>>> mycolor is Color.RED
False
>>> mycolor is Color.GREEN
True

10.1.5. Iterating

Iterating over Enum:

>>> from enum import Enum
>>>
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'
>>>
>>>
>>> for color in Color:
...     print(color)
Color.RED
Color.GREEN
Color.BLUE

10.1.6. Pattern Matching

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

../_images/oop-enum-keycodes.png

Note, keycodes can vary depending on operating system and programming language used [mskeycodes], [jskeycodes].

>>> int('0x1B', base=16)
27
>>>
>>> hex(27)
'0x1b'
>>> from enum import Enum
>>>
>>>
>>> class Key(Enum):
...     ESC = 27            # 0x1B
...     ARROW_LEFT = 37     # 0x25
...     ARROW_UP = 38       # 0x26
...     ARROW_RIGHT = 39    # 0x27
...     ARROW_DOWN = 40     # 0x28
>>>
>>> 
... 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')
>>> 
... 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')

10.1.7. Use Case - HTTP Status

>>> from http import HTTPStatus
>>>
>>>
>>> response = 418
>>>
>>> status = HTTPStatus(response)
>>> print(status.name)
IM_A_TEAPOT

10.1.8. Use Case - Colors

>>> from enum import Enum
>>>
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'
>>>
>>>
>>> Point = tuple[int,int]
>>>
>>> def draw_line(A: Point, B: Point, color: Color):
...     print(f'Drawing line from {A} to {B} with color {color.value}')
>>>
>>>
>>> draw_line(A=(0,0), B=(3,5), color=Color.RED)
Drawing line from (0, 0) to (3, 5) with color #FF0000

10.1.9. Use Case - Health

>>> from enum import Enum
>>>
>>>
>>> class Status(Enum):
...     FULL_HEALTH = 100
...     DEAD = 0
>>>
>>>
>>> hit_points = 100
>>> Status(hit_points)
<Status.FULL_HEALTH: 100>
>>>
>>>
>>> hit_points = 0
>>> Status(hit_points)
<Status.DEAD: 0>

10.1.10. Use Case - Permission

  • r - read

  • w - write

  • x - execute

  • rwx - read, write, execute; 0b111 == 0o7

  • rw- - read, write; 0b110 == 0o6

  • r-x - read, execute; 0b101 == 0o5

  • r-- - read only; 0b100 == 0o4

  • rwxr-xr-- - user=(read,write,execute); group=(read,execute); others=(read)

  • https://docs.python.org/3/library/os.html#os.stat

>>> from enum import Enum
>>> from pathlib import Path
>>>
>>>
>>> class Permission(Enum):
...     READ_WRITE_EXECUTE = 0b111
...     READ_WRITE = 0b110
...     READ_EXECUTE = 0b101
...     READ = 0b100
...     WRITE_EXECUTE = 0b011
...     WRITE = 0b010
...     EXECUTE = 0b001
...     NONE = 0b000
>>>
>>>
>>> file = Path('_temporary.txt')
>>> file.touch()
>>> file.stat()  
os.stat_result(st_mode=33188, st_ino=98480473, st_dev=16777220,
               st_nlink=1, st_uid=501, st_gid=20, st_size=0,
               st_atime=1624458230, st_mtime=1624458230,
               st_ctime=1624458230)
>>>
>>> permissions = file.stat().st_mode
>>> decimal = int(permissions)
>>> octal = oct(permissions)
>>> binary = bin(permissions)
>>> print(f'{decimal=}, {octal=}, {binary}')
decimal=33188, octal='0o100644', 0b1000000110100100
>>>
>>> *_, user, group, others = oct(permissions)
>>> print(f'{user=} {group=} {others=}')
user='6' group='4' others='4'
>>>
>>> Permission(int(user))
<Permission.READ_WRITE: 6>
>>>
>>> Permission(int(group))
<Permission.READ: 4>
>>>
>>> Permission(int(others))
<Permission.READ: 4>
>>>
>>> file.unlink()

10.1.11. Use Case - Drivers

>>> from enum import IntEnum
>>>
>>>
>>> class IndexDrives(IntEnum):
...     ControlWord = 0x6040
...     StatusWord = 0x6041
...     OperationMode = 0x6060

10.1.12. Assignments

Todo

Create assignments

10.1.13. References

mskeycodes

https://docs.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes?redirectedfrom=MSDN

jskeycodes

https://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes