code: def shape(value):
          
          if value.value:
              _assert_is_type('shape.value', value.value, str_types)
              if value.value not in PropertySet._valid_shapes:
                  raise ValueError(value.value + ' is not a valid shape')
docs: ValueRef : string, type of symbol to use
  
          Possible values are ``'circle'`` (default), ``'square'``,
          ``'cross'``, ``'diamond'``, ``'triangle-up'``, and
          ``'triangle-down'``. Only used if ``type`` is ``'symbol'``.