python中的逻辑错误

我正在用python 3.2编写代码，我有一个漂亮的坦克图。我知道怎么把它移到左边写。然而，当试图使坦克上下移动时。我面临的问题是，它上升了，但如果我放手，再按一下上升按钮。它向左拐。这可能很难解释，所以我加入了代码

"""
Programmer: Bert
Tank Run 1
"""

#------------------------------------------------------------------------------
#Importing random modules geddit
from turtle import *
from turtle import Turtle
import turtle
import random

#Welcome Statement and story
input("WELCOME TO TANK RUN 1!! PRESS ENTER TO CONTINUE")
Name = input("Name your Tank: ")
quitFunction = input(
"""The """ + Name + """ is in a battle and heading toward the
enemy base camp so that the """ + Name + """ can blow it up
Get to the base camp and do not let enemy
artillery, or soldiers kill you. Good luck"""
)

#setting up variables
unVar1 = 25
unVar2 = 100
unVar3 = 90
unVar4 = 150
unVar5 = -30
unVar6 = 75
unVar7 = 50
t = Turtle()

#defining shapes
def polySquare(t, x, y, length):
    t.goto(x, y)
    t.setheading(270)
    t.begin_poly()
    for count in range(4):
        t.forward(length)
        t.left(90)
    t.end_poly()
    return t.get_poly()

def polyCircle(t, x, y, radius):
    t.up()
    t.goto(x, y)
    t.down()
    t.hideturtle()
    t.circle(radius)
    t.end_poly()
    return t.get_poly()

def polyRectangle(t, x, y, length1, length2):
    t.goto(x, y)
    t.setheading(270)
    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 drawLine(t, x1, x2, y1, y2):
    t.up()
    t.hideturtle()
    t.goto(x1, y1)
    t.do+wn()
    t.goto(x2, y2)

def tankCursor():
    """
    Create the tank cursor.  An alternate solution is to toss the temporary turtle
    and use the commented out polygon assignments instead of the poly* function calls
    """
    temporary = turtle.Turtle()
    screen = turtle.getscreen()
    delay = screen.delay()
    screen.delay(0)
    temporary.hideturtle()
    temporary.penup()
    tank = turtle.Shape("compound")
    # tire1 = ((10, unVar1), (10, unVar1 - unVar6), (10 + 30, unVar1 - unVar6), (10 + 30, unVar1))
    tire1 = polyRectangle(temporary, 10, unVar1, unVar6, 30)  # Tire #1
    tank.addcomponent(tire1, "gray", "black")
    # tire2 = ((110, unVar1), (110, unVar1 - unVar6), (110 + 30, unVar1 - unVar6), (110 + 30, unVar1))
    tire2 = polyRectangle(temporary, 110, unVar1, unVar6, 30)  # Tire #2
    tank.addcomponent(tire2, "gray", "black")
    # tire3 = ((110, unVar2), (110, unVar2 - unVar6), (110 + 30, unVar2 - unVar6), (110 + 30, unVar2))
    tire3 = polyRectangle(temporary, 110, unVar2, unVar6, 30)  # Tire #3
    tank.addcomponent(tire3, "gray", "black")
    # tire4 = ((10, unVar2), (10, unVar2 - unVar6), (10 + 30, unVar2 - unVar6), (10 + 30, unVar2))
    tire4 = polyRectangle(temporary, 10, unVar2, unVar6, 30)  # Tire #4
    tank.addcomponent(tire4, "gray", "black")
    # bodyTank = ((20, unVar3), (20, unVar3 - 130), (20 + 110, unVar3 - 130), (20 + 110, unVar3))
    bodyTank = polyRectangle(temporary, 20, unVar3, 130, 110)
    tank.addcomponent(bodyTank, "black", "gray")
    # gunTank = ((65, unVar4), (65, unVar4 - 100), (65 + 20, unVar4 - 100), (65 + 20, unVar4))
    gunTank = polyRectangle(temporary, 65, unVar4, 100, 20)   # Gun
    tank.addcomponent(gunTank, "black", "gray")
    # exhaustTank = ((50, unVar5), (50, unVar5 - 20), (50 + 10, unVar5 - 20), (50 + 10, unVar5))
    exhaustTank = polyRectangle(temporary, 50, unVar5, 20, 10)
    tank.addcomponent(exhaustTank, "black", "gray")
    # turretTank = ((50, unVar7), (50, unVar7 - 50), (50 + 50, unVar7 - 50), (50 + 50, unVar7))
    turretTank = polySquare(temporary, 50, unVar7, 50)  # Turret
    tank.addcomponent(turretTank, "red", "gray")
    turtle.addshape("tank", shape=tank)
    del temporary
    screen.delay(delay)

tankCursor()  # creates and registers the "tank" cursor shape
tank = turtle
tank.shape("tank")

turtle.up()  # get rid of the ink
screen = turtle.Screen()

def moveforward():    #I cannot get this function to work
    tank.left(90)
    tank.forward(40)

def movebackward():    #I cannot get this function to work
    tank.left(90)
    tank.backward(40)

def moveright():
    tank.forward(40)

def moveleft():
    tank.backward(40)

#Background color
t.screen.bgcolor("green")

#Movement of tank
screen.onkeypress(moveright, "Right")
screen.onkeypress(moveleft, "Left")
screen.onkeypress(moveforward, "Up")
screen.onkeypress(movebackward, "Down")

---

绘制自定义光标时，除非有理由不这样做，否则应使光标设计以原点（0，0）为中心。若你们画到原点的一边，那个么当你们的乌龟向右或向左转弯时，它不会对称地这样做。也就是说，当它朝一个方向转弯时，它看起来会很快转弯，但在相反的方向上，它看起来会“走很长的路”

我已经处理了坦克光标下面的多边形，使其中心是炮塔的中心，并从绘图例程中删除了setheading（）调用

这个例子使用了我认为是一致的运动：无论坦克方向如何，“上”是向前，“下”是向后，“左”是向左90度，“右”是向右90度。为了演示这个动作，我还简化了这个例子：

import turtle

# Defining shapes
def 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 shape
turtle.shape("tank")
turtle.up()  # get rid of the ink

# Movement of tank
screen = 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()

---

非常感谢您解决我的问题。@cdlane这将解决OPs问题，但不会解释他们做错了什么或为什么做错了，也不会帮助未来的用户。@XamuelSchulman，我已经修改了我的答案，以更好地解决设计海龟游标的具体问题，该游标的起源是对称的——我希望它能够解决您的合理担忧，即在这个答案中没有足够的带回家的信息给其他人。