text: from pcc.util import Base, PositiveInteger
  
  
  dx: PositiveInteger
  
  
  class Player2(Base):
      # 3.6 class anotations
  
      x: PositiveInteger    # but it can be work
  
      def left(self, dx):
          self.x -= dx
  
  
  def test_contact():
  
      a = Player2(2)  # init can be checked abut a.x can be check?
      # when Player2(1) 1-1 is 0 so it is failed!
      a.left(1)