code: def _return_comma_list(self, l):
          
          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
docs: get a list and return a string with comma separated list values
          Examples ['to', 'ta'] will return 'to,ta'.