4.2. Match Literal
A literal pattern is useful to filter constant values in a
structure. It looks like a Python literal (including some values like
True, False and None). It only matches objects equal to
the literal, and never binds.
4.2.1. Problem
>>> color = 'r'
>>>
>>> if color == 'r':
... print('red')
... elif color == 'g':
... print('green')
... elif color == 'b':
... print('blue')
...
red
4.2.2. Solution
>>> color = 'r'
>>>
>>> match color:
... case 'r': print('red')
... case 'g': print('green')
... case 'b': print('blue')
...
red
4.2.3. String Values
>>> user = 'Mark'
>>>
>>> match user:
... case 'Mark': print('Hello Mark')
... case 'Melissa': print('Hello Melissa')
... case 'Rick': print('Hello Rick')
... case 'Alex': print('Hello Alex')
... case 'Beth': print('Hello Beth')
... case 'Chris': print('Hello Chris')
...
Hello Mark
4.2.4. Numeric Values
>>> weekday = 3
>>>
>>> match weekday:
... case 1: print('Monday')
... case 2: print('Tuesday')
... case 3: print('Wednesday')
... case 4: print('Thursday')
... case 5: print('Friday')
... case 6: print('Saturday')
... case 7: print('Sunday')
...
Wednesday
4.2.5. Logic Values
>>> status = True
>>>
>>> match status:
... case True: print('success')
... case False: print('error')
... case None: print('in-progress')
...
success
4.2.6. Use Case - 1
>>> def weekday(number):
... match number:
... case 1: print('Monday')
... case 2: print('Tuesday')
... case 3: print('Wednesday')
... case 4: print('Thursday')
... case 5: print('Friday')
... case 6: print('Saturday')
... case 7: print('Sunday')
>>> weekday(1)
Monday
>>>
>>> weekday(2)
Tuesday
>>>
>>> weekday(7)
Sunday
4.2.7. Use Case - 2
>>> def html_color(name):
... match name:
... case 'red': return '#ff0000'
... case 'green': return '#00ff00'
... case 'blue': return '#0000ff'
>>>
>>>
>>> html_color('red')
'#ff0000'
>>>
>>> html_color('green')
'#00ff00'
>>>
>>> html_color('blue')
'#0000ff'
4.2.8. Use Case - 3
>>> def status(result):
... match result:
... case True: return 'success'
... case False: return 'error'
... case None: return 'in-progress'
>>>
>>>
>>> status(True)
'success'
>>>
>>> status(False)
'error'
>>>
>>> status(None)
'in-progress'
4.2.9. Use Case - 4
>>> def http_status(status_code):
... match status_code:
... case 400: return 'Bad request'
... case 401: return 'Unauthorized'
... case 402: return 'Payment Required'
... case 403: return 'Forbidden'
... case 404: return 'Not found'
... case 418: return "I'm a teapot"
>>> http_status(400)
'Bad request'
>>>
>>> http_status(403)
'Forbidden'
>>>
>>> http_status(404)
'Not found'
4.2.10. Use Case - 5
>>> def say_hello(language):
... match language:
... case 'English': return 'Hello'
... case 'German': return 'Guten Tag'
... case 'Spanish': return 'Hola'
... case 'Polish': return 'Witaj'
... case _: return "I don't speak this language"
>>> say_hello('English')
'Hello'
>>>
>>> say_hello('Polish')
'Witaj'
>>>
>>> say_hello('French')
"I don't speak this language"
4.2.11. Use Case - 6
>>> def count(*args):
... match len(args):
... case 3: return 'Three'
... case 2: return 'Two'
... case 1: return 'One'
... case 0: return 'Zero'
>>>
>>>
>>> count(1, 2, 3)
'Three'
>>>
>>> count(1, 2)
'Two'
>>>
>>> count(1)
'One'
>>>
>>> count()
'Zero'
4.2.12. Use Case - 7
>>> def myrange(*args, **kwargs):
... if kwargs:
... raise TypeError('myrange() takes no keyword arguments')
...
... match len(args):
... case 3:
... start = args[0]
... stop = args[1]
... step = args[2]
... case 2:
... start = args[0]
... stop = args[1]
... step = 1
... case 1:
... start = 0
... stop = args[0]
... step = 1
... case 0:
... raise TypeError('myrange expected at least 1 argument, got 0')
... case _:
... raise TypeError(f'myrange expected at most 3 arguments, got {len(args)}')
...
... current = start
... result = []
... while current < stop:
... result.append(current)
... current += step
... return result
4.2.13. Use Case - 8
>>> def myrange(*args, **kwargs):
... match len(args):
... case 3:
... start, stop, step = args
... case 2:
... start, stop = args
... step = 1
... case 1:
... start = 0
... stop = args[0]
... step = 1
... case 0:
... raise TypeError('myrange expected at least 1 argument, got 0')
... case _:
... raise TypeError(f'myrange expected at most 3 arguments, got {len(args)}')
... ...
4.2.14. Use Case - 9
>>> def myrange(*args, **kwargs):
... match len(args):
... case 3: start, stop, step = args
... case 2: [start, stop], step = args, 1
... case 1: start, [stop], step = 0, args, 1
... case 0: raise TypeError('myrange expected at least 1 argument, got 0')
... case _: raise TypeError(f'myrange expected at most 3 arguments, got {len(args)}')
... ...
4.2.15. Use Case - 10
>>> import argparse
>>>
>>> parser = argparse.ArgumentParser()
>>> _ = parser.add_argument('command', choices=['push', 'pull', 'commit'])
>>> args = parser.parse_args(['push'])
>>>
>>> match args.command:
... case 'push': print('Pushing...')
... case 'pull': print('Pulling...')
... case _: parser.error(f'{args.command!r} not yet implemented')
...
Pushing...
4.2.16. Assignments
# %% 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
# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`
# %% About
# - Name: Match Literal Color
# - Difficulty: easy
# - Lines: 4
# - Minutes: 3
# %% English
# 1. Refactor `if` statement to `match` statement
# 2. Use a literal pattern
# 3. Run doctests - all must succeed
# %% Polish
# 1. Zrefaktoruj instrukcję warunkową `if` na instrukcję `match`
# 2. Użyj literal pattern
# 3. Uruchom doctesty - wszystkie muszą się powieść
# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 10), \
'Python 3.10+ required'
>>> from pathlib import Path
>>> code = Path(__file__).read_text()
>>> assert 'match' + ' ' + 'color' in code
>>> assert 'case' in code
"""
color = 'r'
# Refactor `if` statement to `match` statement
# Use a literal pattern
if color == 'r':
result = 'red'
elif color == 'g':
result = 'green'
elif color == 'b':
result = 'blue'