10.8. Enum Use Cases

10.8.1. SetUp

>>> from enum import Enum, IntEnum, StrEnum, Flag, IntFlag, auto

10.8.2. Use Case - 1

>>> class Color(Enum):
...     AQUA = '#00FFFF'
...     BLACK = '#000000'
...     BLUE = '#0000ff'
...     FUCHSIA = '#FF00FF'
...     GRAY = '#808080'
...     GREEN = '#008000'
...     LIME = '#00ff00'
...     MAROON = '#800000'
...     NAVY = '#000080'
...     OLIVE = '#808000'
...     PINK = '#ff1a8c'
...     PURPLE = '#800080'
...     RED = '#ff0000'
...     SILVER = '#C0C0C0'
...     TEAL = '#008080'
...     WHITE = '#ffffff'
...     YELLOW = '#FFFF00'

10.8.3. Use Case - 2

>>> class Languages(Enum):
...     EN = 'English'
...     PL = 'Polish'
...     DE = 'German'

10.8.4. Use Case - 3

>>> class Currency(Enum):
...     PLN = 1
...     USD = 4.00
...     EUR = 4.20

10.8.5. Use Case - 4

>>> class CountryCode(Enum):
...     PL = '+48'
...     DE = '+49'
...     US = '+1'

10.8.6. Use Case - 5

>>> class EmailType(Enum):
...     PRIV = 1
...     WORK = 2

10.8.7. Use Case - 6

>>> class PhoneType(Enum):
...     HOME = 1
...     WORK = 2
...     ASSISTANT = 3

10.8.8. Use Case - 7

>>> class AddressType(Enum):
...     BILLING = 1
...     SHIPPING = 2

10.8.9. Use Case - 8

>>> class Gender(Enum):
...     FEMALE = 1
...     MALE = 2
...     OTHER = 3

10.8.10. Use Case - 9

>>> class Settings(Enum):
...     PROJECT_NAME = ...
...     BASE_DIRECTORY = ...
...     STATIC_ROOT = ...

10.8.11. Use Case - 10

>>> class ScreenResolution(Enum):
...     X_MIN = 0
...     X_MAX = 1920
...     Y_MIN = 0
...     Y_MAX = 1080

10.8.12. Use Case - 11

>>> class Polish(Enum):
...     PLEASE = 'proszę'
...     THANKS = 'dziękuję'
...     SORRY = 'przepraszam'

>>> class English(Enum):
...     PLEASE = 'please'
...     THANKS = 'thank you'
...     SORRY = 'I am sorry'

10.8.13. Use Case - 12

>>> class ScrumRole(Enum):
...     PRODUCT_OWNER = 'po'
...     SCRUM_MASTER = 'sm'
...     TEAM_MEMBER = 'tm'

10.8.14. Use Case - 13

>>> class Permissions(Flag):
...     READ = 0b100
...     WRITE = 0b010
...     EXECUTE = 0b001

10.8.15. Use Case - 14

>>> class IssueStatus(Enum):
...     TODO = 'todo'
...     IN_PROGRESS = 'in-progress'
...     IN_REVIEW = 'in-review'
...     IN_TEST = 'in-test'
...     DONE = 'done'
...     REJECTED = 'rejected'

10.8.16. Use Case - 15

Definitions:

>>> class ScrumRole(StrEnum):
...     PRODUCT_OWNER = 'po'
...     SCRUM_MASTER = 'sm'
...     TEAM_MEMBER = 'tm'
>>>
>>>
>>> def assign(user, role):
...     if not isinstance(role, ScrumRole):
...         raise ValueError('Invalid role')
...     user.role = role
>>>
>>>
>>> class User:
...     pass

Usage:

>>> mark = User()
>>> mark.firstname = 'Mark'
>>> mark.lastname = 'Watney'
>>> assign(mark, ScrumRole.PRODUCT_OWNER)
>>>
>>> vars(mark)
{'firstname': 'Mark', 'lastname': 'Watney', 'role': <ScrumRole.PRODUCT_OWNER: 'po'>}

10.8.17. Use Case - 16

>>> Point = tuple[int,int]
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'

>>> def draw_line(A: Point, B: Point, color: Color):
...     if type(color) is not Color:
...         possible = [str(c) for c in Color]
...         raise TypeError(f'Invalid color, possible choices: {possible}')
...     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

>>> draw_line(A=(0,0), B=(3,5), color='red')
Traceback (most recent call last):
TypeError: Invalid color, possible choices: ['Color.RED', 'Color.GREEN', 'Color.BLUE']

10.8.18. Use Case - 17

>>> from dataclasses import dataclass
>>>
>>>
>>> class Role(Enum):
...     USER = 1
...     STAFF = 2
...     ADMIN = 3
>>>
>>>
>>> @dataclass
... class Account:
...     firstname: str
...     lastname: str
...     role: Role
>>>
>>>
>>> mark = Account('Mark', 'Watney', role='not-existing')
>>> mark = Account('Mark', 'Watney', role=Role.USER)

10.8.19. Use Case - 18

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('/tmp/myfile.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()

10.8.20. Use Case - 19

>>> 
... from django.db import models
...
... class HttpMethod(models.TextChoices):
...     GET = 'GET', _('GET')
...     POST = 'POST', _('POST')
...     PATCH = 'PATCH', _('PATCH')
...     PUT = 'PUT', _('PUT')
...     HEAD = 'HEAD', _('HEAD')
...     DELETE = 'DELETE', _('DELETE')
...     OPTIONS = 'OPTIONS', _('OPTIONS')
...     TRACE = 'TRACE', _('TRACE')
...     CONNECT = 'CONNECT', _('CONNECT')
...
...
... class Stage(models.TextChoices):
...     PRODUCTION = 'production', _('Production')
...     TEST = 'test', _('Test')

10.8.21. Use Case - 20

>>> class Planet(Enum):
...     MERCURY = (3.303e+23, 2.4397e6)
...     VENUS   = (4.869e+24, 6.0518e6)
...     EARTH   = (5.976e+24, 6.37814e6)
...     MARS    = (6.421e+23, 3.3972e6)
...     JUPITER = (1.9e+27,   7.1492e7)
...     SATURN  = (5.688e+26, 6.0268e7)
...     URANUS  = (8.686e+25, 2.5559e7)
...     NEPTUNE = (1.024e+26, 2.4746e7)
...
...     def __init__(self, mass, radius):
...         self.mass = mass       # in kilograms
...         self.radius = radius   # in meters
...
...     @property
...     def surface_gravity(self):
...         # universal gravitational constant  (m3 kg-1 s-2)
...         G = 6.67300E-11
...         return G * self.mass / (self.radius * self.radius)

>>> Planet.EARTH.value
(5.976e+24, 6378140.0)
>>>
>>> Planet.EARTH.surface_gravity
9.802652743337129

10.8.22. Use Case - 21

>>> Point = tuple[int,int]
>>>
>>> class Color(Enum):
...     RED = '#FF0000'
...     GREEN = '#00FF00'
...     BLUE = '#0000FF'

>>> def draw_line(A: Point, B: Point, color: Color):
...     if type(color) is not Color:
...         possible = [str(c) for c in Color]
...         raise TypeError(f'Invalid color, possible choices: {possible}')
...     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

>>> draw_line(A=(0,0), B=(3,5), color='red')
Traceback (most recent call last):
TypeError: Invalid color, possible choices: ['Color.RED', 'Color.GREEN', 'Color.BLUE']

10.8.23. Use Case - 22

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('/tmp/myfile.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()

10.8.24. Use Case - 23

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

10.8.25. Use Case - 24

>>> from dataclasses import dataclass
>>>
>>>
>>> class Agency(Enum):
...     NASA = auto()
...     ESA = auto()
...     JAXA = auto()
>>>
>>>
>>> @dataclass
... class Astronaut:
...     firstname: str
...     lastname: str
...     agency: Agency
>>>
>>>
>>> mark = Astronaut('Mark', 'Watney', agency='not-existing')
>>> mark = Astronaut('Mark', 'Watney', agency=Agency.NASA)

10.8.26. Use Case - 25

>>> 
... from django.db import models
...
... class HttpMethod(models.TextChoices):
...     GET = 'GET', _('GET')
...     POST = 'POST', _('POST')
...     PATCH = 'PATCH', _('PATCH')
...     PUT = 'PUT', _('PUT')
...     HEAD = 'HEAD', _('HEAD')
...     DELETE = 'DELETE', _('DELETE')
...     OPTIONS = 'OPTIONS', _('OPTIONS')
...     TRACE = 'TRACE', _('TRACE')
...     CONNECT = 'CONNECT', _('CONNECT')
...
...
... class Stage(models.TextChoices):
...     PRODUCTION = 'production', _('Production')
...     TEST = 'test', _('Test')

10.8.27. Use Case - 26

>>> from enum import IntEnum
>>>
>>> class Permission(IntFlag):
...     READ = 0b100
...     WRITE = 0b010
...     EXECUTE = 0b001

>>> file = Path('/tmp/myfile.txt')
>>> file.touch()
>>>
>>> file.stat()  
os.stat_result(st_mode=33188, st_ino=22078540, st_dev=16777231, st_nlink=1, st_uid=501, st_gid=0, st_size=138, st_atime=1718195813, st_mtime=1718195769, st_ctime=1718195769)
>>>
>>> permissions = file.stat().st_mode
>>>
>>> permissions
33188
>>> oct(permissions)
'0o100644'
>>>
>>> *_, user, group, others = oct(permissions)
>>>
>>> Permission(int(user))
<Permission.READ|WRITE: 6>
>>>
>>> Permission(int(group))
<Permission.READ: 4>
>>>
>>> Permission(int(others))
<Permission.READ: 4>

10.8.28. Use Case - 27

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

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

>>> int('0x1B', base=16)
27
>>>
>>> hex(27)
'0x1b'

>>> 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')

10.8.29. Use Case - 28

https://www.euvat.org/vat-returns-poland/
https://www.infor.pl/akt-prawny/DZU.2019.084.0000816,rozporzadzenie-ministra-finansow-w-sprawie-kas-rejestrujacych.html
§6 pkt. 5 - Rozporządzenie Ministra Finansów z dnia 29 kwietnia 2019 r. w sprawie kas rejestrujących. Dziennik Ustaw - rok 2019 poz. 816
PTU - Podatek od Towarów i Usług (Services and Goods Tax)

../../_images/enum-usecase-biedronka.png

>>> class PTU(Enum):
...     A = 1.23   # VAT 23%
...     B = 1.08   # VAT 8%
...     C = 1.05   # VAT 5%
...     D = 1.00   # VAT 0%
...     E = None   # VAT Exempt
>>>
>>> PLN = 1

>>> shopping_cart = [
...     {'name': 'Bread',   'price': 3.99*PLN, 'ptu': PTU.C},
...     {'name': 'Butter',  'price': 2.69*PLN, 'ptu': PTU.B},
...     {'name': 'Ham',     'price': 5.99*PLN, 'ptu': PTU.A},
...     {'name': 'Cheese',  'price': 4.19*PLN, 'ptu': PTU.B},
... ]

>>> total = sum(product['price'] * product['ptu'].value
...             for product in shopping_cart)

>>> print(f'Total is: {total:.2f} PLN')
Total is: 18.99 PLN

10.8.30. 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