code: def WriteSessionStart(self):
      
      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)
docs: 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.