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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 qr_code(self, instance):
 """ Display picture of QR-code from used secret """

        try:
            return self._qr_code(instance)
        except Exception as err:
            if settings.DEBUG:
                import traceback
                return "<pre>%s</pre>" % traceback.format_exc()