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import asyncio
from contextlib import contextmanager
from typing import Any
from typing import Iterator
class PubSub:
_instance = None
def __init__(self):
self.queues: list[asyncio.Queue] = []
self._history = []
@classmethod
def instance(cls) -> "PubSub":
if cls._instance == None:
cls._instance = cls()
return cls._instance
@classmethod
@contextmanager
def subscribe(cls) -> Iterator[asyncio.Queue]:
queue = asyncio.Queue()
instance = cls.instance()
instance.queues.append(queue)
try:
yield queue
finally:
cls.unsubscribe(queue)
@classmethod
def unsubscribe(cls, queue: asyncio.Queue):
instance = cls.instance()
instance.queues.remove(queue)
del queue
@classmethod
def history(cls):
instance = cls.instance()
return instance._history
@classmethod
async def publish(cls, msg: Any):
instance = cls.instance()
instance._history.append(msg)
for queue in instance.queues:
await queue.put(msg)
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