Display stats to stdout.
        Refresh every duration second.

def update(self,
               stats,
               duration=3):
        """Display stats to stdout.
        Refresh every duration second.
        """
        # Build the stats list
        line = ''
        for plugin, attribute in self.plugins_list:
            # Check if the plugin exist and is enable
            if plugin in stats.getPluginsList() and \
               stats.get_plugin(plugin).is_enable():
                stat = stats.get_plugin(plugin).get_export()
            else:
                continue

            # Build the line to display (header or data)
            if self.header:
                line += self.build_header(plugin, attribute, stat)
            else:
                line += self.build_data(plugin, attribute, stat)

        # Display the line (without the last 'separator')
        printandflush(line[:-1])

        # Display header one time
        self.header = False

        # Wait until next refresh
        if duration > 0:
            time.sleep(duration)