The Event Broadcaster

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant grading.

Domain

Python

Difficulty

medium

Seniority

L4

Problem

Implement an EventEmitter that supports on(event, listener), emit(event, payload), and off(event, listener). Listeners are opaque identifiers (strings in the tests). emit notifies every listener currently subscribed to the event by appending the payload to the result list once per listener (so a 3-listener emit returns [payload, payload, payload]); an emit with no listeners returns []. off removes one matching listener identifier (the first one found if duplicates exist). Then implement a driver event_broadcaster(op_names, op_args) that constructs an EventEmitter when op_names[0] is 'EventEmitter' and dispatches the remaining 'on'/'emit'/'off' ops with their parallel arg lists. Return the list of results in op order: None for the constructor, on, and off; the per-listener payload list for emit.

Summary

Subscribers show up, listen, and sometimes leave.

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