def dataset(self, mess, args):
        """send a csv dataset to your email address
           argument : date1(Y-m-d) date2(Y-m-d) sampling period (seconds)
           ex : dataset 2017-09-01 2017-09-02 600
                """
        knownUsers = self.unPickle("knownUsers")

        if len(args.split(' ')) == 3:
            dstart = args.split(' ')[0].strip().lower()
            dend = args.split(' ')[1].strip().lower()
            step = float(args.split(' ')[2].strip().lower())
        else:
            return 'not enough arguments'

        user = mess.getFrom().getNode()
        if user in knownUsers:
            try:
                dstart = dt.strptime(dstart, "%Y-%m-%d")
            except ValueError:
                return "ValueError : time data '%s'" % dstart + " does not match format '%Y-%m-%d'"

            try:
                dend = dt.strptime(dend, "%Y-%m-%d")
            except ValueError:
                return "ValueError : time data '%s'" % dend + " does not match format '%Y-%m-%d'"

            dataset = Dataset(self, mess.getFrom(), dstart.isoformat(), dend.isoformat(), step)
            dataset.start()
            return "Generating the dataset ..."

        else:
            return "Do I know you ? Send me your email address by using the command record "