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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def Items(self, key):
 """Return items associated with given key. Args: key: The key for which we are finding associated items. Raises: KeyError: If the key is not found in the reservoir. Returns: [list, of, items] associated with that key. """

    with self._mutex:
      if key not in self._buckets:
        raise KeyError('Key %s was not found in Reservoir' % key)
      bucket = self._buckets[key]
    return bucket.Items()