4.5. Enum Flag

  • Flag

  • Flag

  • IntFlag

Flags have an expanded view of aliasing: to be canonical, the value of a flag needs to be a power-of-two value, and not a duplicate name. So, in addition to the Enum definition of alias, a flag with no value (a.k.a. 0) or with more than one power-of-two value (e.g. 3) is considered an alias.

SetUp:

>>> from enum import Flag

Definition:

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

Usage:

>>> Permission(1)
<Permission.EXECUTE: 1>
>>>
>>> Permission(2)
<Permission.WRITE: 2>
>>>
>>> Permission(3)
<Permission.WRITE|EXECUTE: 3>
>>>
>>> Permission(4)
<Permission.READ: 4>
>>>
>>> Permission(5)
<Permission.READ|EXECUTE: 5>
>>>
>>> Permission(6)
<Permission.READ|WRITE: 6>
>>>
>>> Permission(7)
<Permission.READ|WRITE|EXECUTE: 7>

Example:

>>> permission = Permission.READ | Permission.WRITE
>>> permission
<Permission.READ|WRITE: 6>

4.5.1. SetUp

>>> from enum import Flag

4.5.2. Recap

  • -rw-r--r--  1 matt 5.0K 2024-06-27 20:06  README.rst

  • user = rw- = 0b110 = 6

  • group = r-- = 0b100 = 4

  • others = r-- = 0b100 = 4

4.5.3. Example

>>> class Permission(Flag):
...     READ = 4
...     WRITE = 2
...     EXECUTE = 1
>>>
>>>
>>> myfile = Permission(5)
>>>
>>> myfile
<Permission.READ|EXECUTE: 5>

4.5.4. Flag

>>> class Permission(Flag):
...     READ = 0b100
...     WRITE = 0b010
...     EXECUTE = 0b001
>>>
>>>
>>> myfile = Permission(5)
>>>
>>> myfile
<Permission.READ|EXECUTE: 5>

4.5.5. Assignments

# %% About
# - Name: Enum Flag Define
# - Difficulty: easy
# - Lines: 4
# - Minutes: 3

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Define enum `Permission`:
# - name: READ, value: 0b100
# - name: WRITE, value: 0b010
# - name: EXECUTE, value: 0b001
# 2. Use `Flag`
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj enum `Permission`:
# - nazwa: READ, wartość: 0b100
# - nazwa: WRITE, wartość: 0b010
# - nazwa: EXECUTE, wartość: 0b001
# 2. Użyj `Flag`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> assert Flag in Permission.mro(), \
'Permission must be an Flag'

>>> assert len(Permission) == 3, \
'Permission must have 3 elements'

>>> assert hasattr(Permission, 'READ')
>>> assert hasattr(Permission, 'WRITE')
>>> assert hasattr(Permission, 'EXECUTE')

>>> assert Permission.READ.value == 0b100
>>> assert Permission.WRITE.value == 0b010
>>> assert Permission.EXECUTE.value == 0b001
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports
from enum import Flag

# %% Types
Permission: type[Flag]

# %% Data

# %% Result