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https://github.com/rjNemo/design-patterns
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* doc: create package & update general TOCs * doc: add documentation * add code example * reformat using black
61 lines
1.7 KiB
Python
61 lines
1.7 KiB
Python
from random import randrange
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from typing import List, Optional
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from behavioral.observer.observer import Observer
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from behavioral.observer.subject import Subject
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class ConcreteSubject(Subject):
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"""
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The Subject owns some important state and notifies observers when the state
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changes.
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"""
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"""
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For the sake of simplicity, the Subject's state, essential to all
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subscribers, is stored in this variable.
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"""
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_state: Optional[int] = None
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"""
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List of subscribers. In real life, the list of subscribers can be stored
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more comprehensively (categorized by event type, etc.).
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"""
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_observers: List[Observer] = []
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@property
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def state(self) -> int:
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return self._state
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def attach(self, observer: Observer) -> None:
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print("Subject: Attached an observer.")
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self._observers.append(observer)
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def detach(self, observer: Observer) -> None:
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self._observers.remove(observer)
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"""
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The subscription management methods.
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"""
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def notify(self) -> None:
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"""
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Trigger an update in each subscriber.
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"""
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print("Subject: Notifying observers...")
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for observer in self._observers:
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observer.update(self)
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def some_business_logic(self) -> None:
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"""
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Usually, the subscription logic is only a fraction of what a Subject can
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really do. Subjects commonly hold some important business logic, that
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triggers a notification method whenever something important is about to
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happen (or after it).
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"""
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print("\nSubject: I'm doing something important.")
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self._state = randrange(0, 10)
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print(f"Subject: My state has just changed to: {self._state}")
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self.notify()
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