code: def represent_list(self, data):
          
          node = super(Dumper, self).represent_list(data)
          length = len(data)
          if self.default_flow_style is None and length < 4:
              node.flow_style = True
          elif self.default_flow_style is None:
              node.flow_style = False
          return node
docs: If a list has less than 4 items, represent it in inline style
          (i.e. comma separated, within square brackets).