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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 GetSessions(self):
 """Retrieves the sessions. Yields: Session: session attribute container. Raises: IOError: if there is a mismatch in session identifiers between the session start and completion attribute containers. OSError: if there is a mismatch in session identifiers between the session start and completion attribute containers. """

    session_start_generator = self._GetAttributeContainers(
        self._CONTAINER_TYPE_SESSION_START)
    session_completion_generator = self._GetAttributeContainers(
        self._CONTAINER_TYPE_SESSION_COMPLETION)

    for session_index in range(0, self._last_session):
      session_start = next(session_start_generator)  # pylint: disable=stop-iteration-return
      session_completion = next(session_completion_generator)  # pylint: disable=stop-iteration-return

      session = sessions.Session()
      session.CopyAttributesFromSessionStart(session_start)
      if session_completion:
        try:
          session.CopyAttributesFromSessionCompletion(session_completion)
        except ValueError:
          raise IOError(
              'Session identifier mismatch for session: {0:d}'.format(
                  session_index))

      yield session