3.10. Match Guard¶
Additional if statements
This is not to replace if-else expression
This add additional validation to match-case
>>> data = [1, 2]
>>>
>>> match data:
... case [x, y] if x > 1024 and y > 1024:
... print('Got a pair of large numbers')
... case [x, y] if x > 1024:
... print('X is a large number')
... case [x, y] if y > 1024:
... print('Y is a large number')
... case [x, y] if x == y:
... print('Got equal items')
... case _:
... print('Not an outstanding input')
Not an outstanding input
3.10.1. Use Case - 0x01¶
>>> def status(health):
... match health:
... case hp if hp <= 0: return 'dead'
... case hp if hp < 50: return 'low'
... case hp if hp >= 50: return 'high'
>>> status(100)
'high'
>>>
>>> status(25)
'low'
>>>
>>> status(10)
'low'
>>>
>>> status(0)
'dead'
>>>
>>> status(-5)
'dead'
3.10.2. Use Case - 0x02¶
>>> ADMINS = ['mlewis', 'bjohanssen']
>>> STAFF = ['mwatney', 'mlewis', 'rmartinez', 'bjohanssen', 'cbeck']
>>>
>>> def login(username, password):
... match username:
... case _ if username in ADMINS:
... print('Admin logged-in')
... case _ if username in STAFF:
... print('Staff logged-in')
... case _ if username not in STAFF:
... raise PermissionError('Access denied')
>>> login('mlewis', 'NASA')
Admin logged-in
>>> login('mwatney', 'Ares3')
Staff logged-in
>>> login('avogel', 'ESA')
Traceback (most recent call last):
PermissionError: Access denied
3.10.3. Use Case - 0x03¶
status "Full Health" - when health 100%
status "Injured" - when health 75% - 100% (exclusive)
status "Badly Wounded" - when health 25% - 75% (exclusive)
status "Near Death" - when health 1% - 25% (exclusive)
status "Dead" - when health 0% or less
>>> hero = ['health', 10]
>>>
>>>
>>> match hero:
... case ['health', percent] if percent == 100:
... status = 'Full health'
...
... case ['health', percent] if percent in range(75, 100):
... status = 'Injured'
...
... case ['health', percent] if percent in range(25, 75):
... status = 'Badly Wounded'
...
... case ['health', percent] if percent in range(1, 25):
... status = 'Near Death'
...
... case ['health', percent] if percent <= 0:
... status = 'Dead'
...
>>> print(status)
Near Death
3.10.4. Use Case - 0x04¶
Game Controller
Test Setup:
>>> class Hero:
... def make_normal_damage(self, dmg): ...
... def make_critical_damage(self, dmg): ...
>>>
>>> hero = Hero()
Use Case:
>>> action = ['make_damage', 5]
>>>
>>>
>>> match action:
...
... case ['make_damage', value] if value >= 10:
... hero.make_critical_damage(value)
...
... case ['make_damage', value] if 0 <= value < 10:
... hero.make_normal_damage(value)
...
... case ['make_damage', value] if value < 0:
... raise ValueError('Damage cannot be negative')
3.10.5. Use Case - 0x05¶
Game Controller
Test Setup:
>>> class Hero:
... def walk(self, direction, value): ...
... def run(self, direction): ...
>>>
>>> hero = Hero()
Use Case:
>>> action = ['move', 'left', 10]
>>>
>>>
>>> match action:
...
... case ['move', direction, speed] if speed < 10:
... hero.walk(direction)
...
... case ['move', direction, speed] if speed >= 10:
... hero.run(direction)
3.10.6. Use Case - 0x06¶
Game Controller
Test Setup:
>>> class Hero:
... def move(self, direction, value): ...
>>>
>>> hero = Hero()
Use Case:
>>> action = ['move', 'left', 10]
>>>
>>>
>>> match action:
...
... case ['move', direction, value] if direction not in ['up','down','left','right']:
... raise ValueError('Invalid direction')
...
... case ['move', direction, value] if direction in ['up','down','left','right']:
... hero.move(direction, value)