In my code I've resolved in this way:
var currentScaleX
var currentScaleY
func _ready():
var currentScale = self.get_scale()
currentScaleX = currentScale.x
currentScaleY = currentScale.y
func _process(delta):
if ( move_to_right ):
self.set_scale(Vector2(-currentScaleX,currentScaleY))
elif ( move_to_left ):
self.set_scale(Vector2(currentScaleX,currentScaleY))
else:
( idle )
-j