Note: your use of
set_position() is incorrect - it takes a single argument of a Vector2, not two arguments.
position property is preferred. Properties will be suggested by autocomplete.
get_ functions were used in Godot pre-3.0 - and still exist for compatibility - but they just make your code more verbose. Compare:
$Node2D.set_position($Node2D.get_position() + Vector2(100, 0))
$Node2D.position += Vector2(100, 0)