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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 WriteSessionStart(self):
 """Writes session start information. Raises: IOError: if the storage type is not supported or when the storage writer is closed. OSError: if the storage type is not supported or when the storage writer is closed. """

    self._RaiseIfNotWritable()

    if self._storage_type != definitions.STORAGE_TYPE_SESSION:
      raise IOError('Unsupported storage type.')

    session_start = self._session.CreateSessionStart()
    self._storage_file.WriteSessionStart(session_start)