Can't render to Sprite
Sprites can only be static or dynamic (init() passed a boolean, "static"). The problem with this is that it doesn't allow you to create the texture with the other option: SDL_TEXTUREACCESS_TARGET (which must be set to render to the texture).
I've monkey-patched Sprite/SpriteFactory in my code to replace the static option with a more sensible access=Sprite.ACCESS_STATIC, Sprite.ACCESS_STREAMING or Sprite.ACCESS_TARGET (where Sprite.ACCESS_TARGET = sdl2.SDL_TEXTUREACCESS_TARGET). Not sure if this is how you'd want it done in pysdl2 ext though.