事件驱动环境中的Python Turtle ` `While True`

Question

我在Stack Overflow上读到过几篇文章，“像turtle这样的事件驱动环境永远不应该有while True:，因为它可能会阻塞事件(例如键盘)。”

下面是一个Python Turtle程序，它看起来工作得很好，但它使用了while True:构造。

谁能解释一下为什么这种方法是错误的，它造成了什么问题，正确的方法是什么才能达到同样的结果？

import turtle
import time


def move_snake():
    """
    This function updates the position of the snake's head according to its direction.
    """
    if head.direction == "up":
        head.sety(head.ycor() + 20)

def go_up():
    """
    callback for up key.
    """
    if head.direction != "down":
        head.direction = "up"

# Set up screen
screen = turtle.Screen()
screen.tracer(0)  # Disable animation so we can update screen manually.

# Event handlers
screen.listen()
screen.onkey(go_up, "Up")

# Snake head
head = turtle.Turtle()
head.shape("square")
head.penup()
head.direction = "stopped"  # Cheeky use of instance property to avoid global variable.


while True:
    move_snake()
    screen.update()
    time.sleep(0.2)

turtle.done()

Answer 1

我可以提供一个粗略的例子。按原样运行上面的代码。让蛇开始移动。单击窗口的关闭按钮。统计您在控制台得到的错误消息行数。它很容易就会超过24个。

现在用下面的代码尝试相同的实验，它消除了while True:

from turtle import Screen, Turtle

class Head(Turtle):
    def __init__(self):
        super().__init__(shape="square")

        self.penup()

        self.direction = "stopped"

def move_snake():
    if head.direction == "up":
        head.sety(head.ycor() + 20)
        screen.update()

    screen.ontimer(move_snake, 200)

def go_up():
    if head.direction != "down":
        head.direction = "up"

# Snake head
head = Head()

# Set up screen
screen = Screen()
screen.tracer(0)  # Disable animation so we can update screen manually.

# Event handlers
screen.onkey(go_up, "Up")
screen.listen()

move_snake()

screen.mainloop()

您的错误消息计数应降至零。这是因为窗口关闭事件发生在与海龟运动相同的事件循环中。

还有一些其他的效果，你稍后会去追逐。这只是一个简单的，容易看到的。