<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def listProcessingEras(self, processing_version=''):
 """ Returns all processing eras in dbs """

        conn = self.dbi.connection()
        try:
            result = self.pelst.execute(conn, processing_version)
            return result
        finally:
            if conn:
                conn.close()