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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 add_dnc( self, obj_id, channel='email', reason=MANUAL, channel_id=None, comments='via API' ):
 """ Adds Do Not Contact :param obj_id: int :param channel: str :param reason: str :param channel_id: int :param comments: str :return: dict|str """

        data = {
            'reason': reason,
            'channelId': channel_id,
            'comments': comments
        }
        response = self._client.session.post(
            '{url}/{id}/dnc/add/{channel}'.format(
                url=self.endpoint_url, id=obj_id, channel=channel
            ),
            data=data
        )
        return self.process_response(response)