乌龟定义的函数没有一次执行所有代码

Question

我正在尝试编写一个程序，允许我使用 turtle 模块绘制一些简单的坐标，并使其更加用户友好，我希望每次用户按下鼠标左键绘制一个点时都显示一个十字。由于某种原因，cross() 函数的最后一位，即。在再次按下鼠标左键之前，十字的最后一行不会绘制或出现。我真的很困惑为什么会发生这种情况，因为代码肯定正在执行。任何帮助将不胜感激！

wn = t.Screen()
wn.title("graph")
wn.setup(width=600, height=600)
wn.tracer(0)
wn.update()

pen = t.Turtle()
pen.color("black")
pen.shape("classic")
pen.goto(0, 0)
pen.ht()

x = 10
y = 10

def cross(x, y):
    print(x, y)
    pen.pensize(2.5)
    pen.pu()
    pen.goto(x, y)
    pen.pd()
    pen.seth(225)
    pen.color("red")
    pen.fd(50)
    pen.color("black")

    pen.pu()
    pen.goto(x, y)
    pen.pd()
    pen.left(180)
    pen.fd(50)

    pen.pu()
    pen.goto(x, y)
    pen.seth(315)
    pen.pd()
    pen.color("green")
    pen.fd(50)

    pen.pu()
    pen.goto(x, y)
    pen.left(180)
    pen.pd()
    pen.color("yellow")
    pen.fd(50) #for some reason this is not being done
    print("now")

cross(x, y)

while True:
    wn.update()
    wn.onscreenclick(cross)
    wn.mainloop()

Answer 1

此代码表明对onscreenclick() 和mainloop() 所做的事情的基本误解：

while True:
    wn.update()
    wn.onscreenclick(cross)
    wn.mainloop()

让我们重新编写代码以正确使用这些方法，并修复问题：

from turtle import Screen, Pen

def cross(x, y):
    screen.onclick(None)  # disable handler inside handler

    pen.penup()
    pen.goto(x, y)
    pen.pendown()
    pen.setheading(225)
    pen.color('red')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.pendown()
    pen.left(180)
    pen.color('black')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.seth(315)
    pen.pendown()
    pen.color('green')
    pen.forward(50)

    pen.penup()
    pen.goto(x, y)
    pen.left(180)
    pen.pendown()
    pen.color('yellow')
    pen.forward(50)

    screen.update()
    screen.onclick(cross)  # reenable handler on exit

screen = Screen()
screen.title("graph")
screen.setup(width=600, height=600)
screen.tracer(0)

pen = Pen()
pen.hideturtle()
pen.color('black')
pen.pensize(2.5)

x, y = 10, 10

screen.onclick(cross)

cross(x, y)

screen.mainloop()

一般来说，我会避免使用tracer() 和update()，直到您的代码基本正常工作。从一开始就加入它们会使您的代码更难调试。