get a list and return a string with comma separated list values
        Examples ['to', 'ta'] will return 'to,ta'.

def _return_comma_list(self, l):
        """ get a list and return a string with comma separated list values
        Examples ['to', 'ta'] will return 'to,ta'.
        """
        if isinstance(l, (text_type, int)):
            return l

        if not isinstance(l, list):
            raise TypeError(l, ' should be a list of integers, \
not {0}'.format(type(l)))

        str_ids = ','.join(str(i) for i in l)

        return str_ids