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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 timeframe(self, start, end):
 r""" When you want to search bugs for a certain time frame. :param start: :param end: :returns: :class:`Search` """

        if start:
            self._time_frame['chfieldfrom'] = start
        if end:
            self._time_frame['chfieldto'] = end
        return self