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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 FetchCompletedRequests(self, session_id, timestamp=None):
 """Fetch all the requests with a status message queued for them."""

    if timestamp is None:
      timestamp = (0, self.frozen_timestamp or rdfvalue.RDFDatetime.Now())

    for request, status in self.data_store.ReadCompletedRequests(
        session_id, timestamp=timestamp, limit=self.request_limit):
      yield request, status