import time
import threading

class TranscriptionDict:
    def __init__(self, max_size=1000):
        self.max_size = max_size
        self._dict = {}

        # Start a thread to clean expired items every 3 minutes
        self._clean_thread = threading.Thread(target=self._clean_expired_items_periodically)
        self._clean_thread.daemon = True
        self._clean_thread.start()

    def __len__(self):
        return len(self._dict)

    def get(self, key):
        return self._dict[key]

    def set(self, key, value):
        self._dict[key] = value
        if len(self._dict) > self.max_size:
            self._clean_expired_items()

    def __contains__(self, key):
        return key in self._dict

    def _clean_expired_items(self):
        now = time.time()
        expired_items = [k for k, v in self._dict.items() if now - v[1] >= 180] # 180 seconds = 3 minutes
        for key in expired_items:
            del self._dict[key]

    def _clean_expired_items_periodically(self):
        while True:
            time.sleep(180)  # Check for expired items every 3 minutes
            self._clean_expired_items()