python乌龟中的逻辑错误

绘制自定义光标时，除非有理由不这样做，否则请使光标设计以原点（0，0）为中心。如果您绘制到原点的一侧，那么当您的海龟向右或向左转时，它不会对称地这样做。就是说，当它朝一个方向转动时，它看起来会很快，但是朝相反的方向，它将看起来“走很远”。

我已经处理了坦克光标下方的多边形，以使其中心为炮塔的中心，并从绘制例程中删除了setheading（）调用。

这个示例使用了我认为是一致的运动：无论油箱方向如何，“上”是向前，“下”是后向，“左”是左90度，“右”是右90度。我还精简了示例，以演示运动：

import turtle# Defining shapesdef polySquare(t, x, y, length):    t.goto(x, y)    t.begin_poly()    for count in range(4):        t.forward(length)        t.left(90)    t.end_poly()    return t.get_poly()def polyRectangle(t, x, y, length1, length2):    t.goto(x, y)    t.begin_poly()    for count in range(2):        t.forward(length1)        t.left(90)        t.forward(length2)        t.left(90)    t.end_poly()    return t.get_poly()def tankCursor():    """    Create the tank cursor.    """    temporary = turtle.Turtle()    temporary.hideturtle()    temporary.penup()    screen = turtle.getscreen()    delay = screen.delay()    screen.delay(0)    tank = turtle.Shape("compound")    tire1 = polyRectangle(temporary, -65, -75, 30, 75)  # Tire #1    tank.addcomponent(tire1, "gray", "black")    tire2 = polyRectangle(temporary, 35, -75, 30, 75)  # Tire #2    tank.addcomponent(tire2, "gray", "black")    tire3 = polyRectangle(temporary, 35, 0, 30, 75)  # Tire #3    tank.addcomponent(tire3, "gray", "black")    tire4 = polyRectangle(temporary, -65, 0, 30, 75)  # Tire #4    tank.addcomponent(tire4, "gray", "black")    bodyTank = polyRectangle(temporary, -55, -65, 110, 130)    tank.addcomponent(bodyTank, "black", "gray")    gunTank = polyRectangle(temporary, -10, 25, 20, 100)   # Gun    tank.addcomponent(gunTank, "black", "gray")    exhaustTank = polyRectangle(temporary, -25, -75, 10, 20)    tank.addcomponent(exhaustTank, "black", "gray")    turretTank = polySquare(temporary, -25, -25, 50)  # Turret    tank.addcomponent(turretTank, "red", "gray")    turtle.addshape("tank", shape=tank)    del temporary    screen.delay(delay)tankCursor()  # creates and registers the "tank" cursor shapeturtle.shape("tank")turtle.up()  # get rid of the ink# Movement of tankscreen = turtle.Screen()screen.onkeypress(lambda : turtle.right(90), "Right")screen.onkeypress(lambda : turtle.left(90), "Left")screen.onkeypress(lambda : turtle.forward(40), "Up")screen.onkeypress(lambda : turtle.backward(40), "Down")turtle.listen()turtle.mainloop()