## Problem Implement a `Subject` class (observable) and a `Subscription` class (observer handle) following the observer pattern. Multiple observers can subscribe to a subject; each receives emitted values. Subscribers can unsubscribe at any time. ```python class Subscription: def unsubscribe(self): ... class Subject: def subscribe(self, on_next, on_error=None, on_complete=None) -> Subscription: ... def next(self, value): ... def error(self, err): ... def complete(self): ... ``` **Example:** ``` subj = Subject() values = [] sub = subj.subscribe(on_next=lambda v: values.append(v)) subj.next(1) subj.next(2) sub.unsubscribe() subj.next(3) # not received print(values) # [1, 2] ``` **Additional requirement:** After `complete()` or `error()` is called, subsequent `next()` calls are no-ops and new subscribers immediately receive the terminal event. ## Follow-ups 1. How would you add back-pressure support if the subscriber is slower than the producer? 2. Implement a `pipe(operator)` method that applies a transform (e.g., `map`, `filter`) to the subject's stream. 3. How does this pattern differ from Python's `asyncio` event streams? 4. How would you make `subscribe` and `next` thread-safe?

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Subscription and Subject Class - Implement an Observable/Observer Pattern

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Problem Implement a Subject class (observable) and a Subscription class (observer handle) following the observer pattern. Multiple observers can subscribe to a subject; each receives emitted values. Subscribers can unsubscribe at any time. Example: Additional requirement: After complete() or error() is called, subsequent next() calls are no-ops and new subscribers immediately receive the terminal event. Follow-ups How would you add back-pressure support if the subscriber is slower than the produ…

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Subscription and Subject Class - Implement an Observable/Observer Pattern

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