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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 update(self, stats):
 """Update stats in the CSV output file."""

        # Get the stats
        all_stats = stats.getAllExportsAsDict(plugin_list=self.plugins_to_export())

        # Init data with timestamp (issue#708)
        if self.first_line:
            csv_header = ['timestamp']
        csv_data = [time.strftime('%Y-%m-%d %H:%M:%S')]

        # Loop over plugins to export
        for plugin in self.plugins_to_export():
            if isinstance(all_stats[plugin], list):
                for stat in all_stats[plugin]:
                    # First line: header
                    if self.first_line:
                        csv_header += ('{}_{}_{}'.format(
                            plugin, self.get_item_key(stat), item) for item in stat)
                    # Others lines: stats
                    csv_data += itervalues(stat)
            elif isinstance(all_stats[plugin], dict):
                # First line: header
                if self.first_line:
                    fieldnames = iterkeys(all_stats[plugin])
                    csv_header += ('{}_{}'.format(plugin, fieldname)
                                   for fieldname in fieldnames)
                # Others lines: stats
                csv_data += itervalues(all_stats[plugin])

        # Export to CSV
        if self.first_line:
            self.writer.writerow(csv_header)
            self.first_line = False
        self.writer.writerow(csv_data)
        self.csv_file.flush()