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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 complete_transfer(self, relation, cleanup=True):
 """Write records to the data source indicating that a transfer has been completed for a particular relation. """

    relation.completed_at = utc_now().isoformat()
    self.data_access.update_model(relation)
    if cleanup:
      self.cleanup()
    return relation