Python Add-In Q: Polygons

I need to replicate the Select By Polygon tool (minus the selecting step). I simply need to be able to draw a temporary polygon to 'do stuff' with. What am I missing here? --- I see a way to set self.shape to Line, Circle or Rectanlge but there is no Polygon.

I can set self.shape to "Line" and then create an array of points in the onLine def, but this is not what the SelectByPolygon tool is doing.

Please help with this seemingly simple process.

Thanks!
j