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from abc import ABC, abstractmethod |
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from typing import List |
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__all__ = ['Subject', 'Observer'] |
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class ObserverInterface(ABC): |
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"""The Observer interface declares the update method, used by subjects. Whenever an 'event' happens the update |
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callback executes.""" |
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@abstractmethod |
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def update(self, *args, **kwargs) -> None: |
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"""Receive update from subject.""" |
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raise NotImplementedError |
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class SubjectInterface(ABC): |
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"""The Subject interface declares a set of methods for managing subscribers. |
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Use it to model objects as "subjects of observations" (notify observers/listeners/subscribers). |
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""" |
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@abstractmethod |
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def attach(self, observer: ObserverInterface) -> None: |
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"""Attach an observer to the subject.""" |
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raise NotImplementedError |
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@abstractmethod |
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def detach(self, observer: ObserverInterface) -> None: |
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"""Detach an observer from the subject.""" |
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raise NotImplementedError |
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@abstractmethod |
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def notify(self) -> None: |
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"""Notify all observers about an event.""" |
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raise NotImplementedError |
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class Subject(SubjectInterface): |
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"""The Subject owns some important state and notifies observers when the state changes. Both the _state and _observers |
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attributes can be overriden to accomodate for more complex scenarios.""" |
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def __new__(cls, *args, **kwargs): |
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self_object = super().__new__(cls) |
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self_object._observers = [] # type=List[ObserverInterface] |
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self_object._state = None |
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return self_object |
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def add(self, *observers): |
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self._observers.extend([_ for _ in observers]) |
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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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@property |
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def state(self): |
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return self._state |
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@state.setter |
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def state(self, state): |
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self._state = state |
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def attach(self, observer: ObserverInterface) -> None: |
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self._observers.append(observer) |
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print(f"\nATTACH:\nSubject:\n{self}\nOBSERVED BY\n{observer}") |
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def detach(self, observer: ObserverInterface) -> 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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"""Trigger an update in each subscriber/observer.""" |
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for observer in self._observers: |
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observer.update(self) |
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""" |
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Concrete Observers react to the updates issued by the Subject they had been |
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attached to. |
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""" |
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class Observer(ObserverInterface): |
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def update(self, subject: Subject) -> None: |
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pass |
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boromir674 /
so-magic
