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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 _process_stages(self, limit=None):
 """ This table provides mappings between ZFIN stage IDs and ZFS terms, and includes the starting and ending hours for the developmental stage. Currently only processing the mapping from the ZFIN stage ID to the ZFS ID. :param limit: :return: """


        if self.test_mode:
            graph = self.testgraph
        else:
            graph = self.graph
        model = Model(graph)
        LOG.info("Processing stages")
        line_counter = 0
        raw = '/'.join((self.rawdir, self.files['stage']['file']))
        with open(raw, 'r', encoding="iso-8859-1") as csvfile:
            filereader = csv.reader(csvfile, delimiter='\t', quotechar='\"')
            for row in filereader:
                line_counter += 1
                (stage_id, stage_obo_id, stage_name, begin_hours, end_hours
                 # ,empty  # till next time
                ) = row

                # Add the stage as a class, and it's obo equivalent
                stage_id = 'ZFIN:' + stage_id.strip()
                model.addClassToGraph(stage_id, stage_name)
                model.addEquivalentClass(stage_id, stage_obo_id)

                if not self.test_mode and limit is not None and line_counter > limit:
                    break

        LOG.info("Done with stages")
        return