You're declaring _animated_sprite as a property (variable), but trying to use it as a method (function).
My guess is that:
_animated_sprite("right")
should be:
_animated_sprite.play("right")
But it looks strange that an AnimatedSprite has a child that's also an AnimatedSprite. If there's only one AnimatedSprite node and that script is attached to it, then you don't need the variable _animated_sprite.
If that's the case, change:
_animated_sprite("right")
to:
play("right")