code: def marker(self, marker_name=None, label=None, 
                 color=None, retina=False):
          
  
          # Check for marker_name.
  
          if marker_name is None:
              raise ValidationError(
                  "marker_name is a required argument"
              )
  
          # Validate marker_name and retina.
  
          marker_name = self._validate_marker_name(marker_name)
          retina = self._validate_retina(retina)
  
          # Create dict and start building URI resource path.
  
          path_values = dict(
              marker_name=marker_name
          )
  
          path_part = "/marker/{marker_name}"
  
          # Validate label, update dict,
          # and continue building URI resource path.
  
          if label is not None:
              label = self._validate_label(label)
              path_values["label"] = label
              path_part += "-{label}"
  
          # Validate color, update dict,
          # and continue building URI resource path.
  
          if color is not None:
              color = self._validate_color(color)
              path_values["color"] = color
              path_part += "+{color}"
  
          uri = URITemplate(self.base_uri + path_part).expand(**path_values)
  
          # Finish building URI resource path.
  
          path_part = "{}.png".format(retina)
          uri += path_part
  
          # Send HTTP GET request.
  
          response = self.session.get(uri)
          self.handle_http_error(response)
  
          return response
docs: Returns a single marker image without any
             background map.
  
          Parameters
          ----------
          marker_name : str
              The marker's shape and size.
  
          label : str, optional
              The marker's alphanumeric label.
  
              Options are a through z, 0 through 99, or the
              name of a valid Maki icon.
  
          color : str, optional
              The marker's color.
  
              Options are three- or six-digit hexadecimal
              color codes.
  
          retina : bool, optional
              The marker's scale, where True indicates Retina scale
              (double scale) and False indicates regular scale.  
  
              The default value is false.
   
          Returns
          -------
          request.Response
              The response object with the specified marker.