Python，乌龟不会出现，并且不会响应键盘控件

Question

I'm trying to make a Python program where a player controls a turtle (from the 'turtle' module) to reach a goal, avoiding an obstacle along the way.

The code for the obstacle and goal drawing works fine, however for some reason the player turtle is not visible and will not respond to keyboard commands. I've elected to not include the entire code and will instead include only the relevant sections. Below is the code for the player controls. The player is setup as a turtle already and screen is setup with screen = turtle.Screen() . I recieve no errors when I try to run it. I will leave the link to the code on my github if anyone would like to have a look at it.

speed = 1


def travel():
    player.forward(speed)
    screen.ontimer(travel, 10)


player.pendown()
player.forward(10)
screen.onkey(lambda: player.setheading(90), 'Up')
screen.onkey(lambda: player.setheading(180), 'Left')
screen.onkey(lambda: player.setheading(0), 'Right')
screen.onkey(lambda: player.setheading(270), 'Down')

screen.listen()

travel()

screen.mainloop()

Answer 1

Once complete, your example works fine:

from turtle import Turtle, Screen

def travel():
    player.forward(1)
    screen.ontimer(travel, 10)

screen = Screen()
player = Turtle()

screen.onkey(lambda: player.setheading(0), 'Right')
screen.onkey(lambda: player.setheading(90), 'Up')
screen.onkey(lambda: player.setheading(180), 'Left')
screen.onkey(lambda: player.setheading(270), 'Down')

screen.listen()

travel()

screen.mainloop()

As far as your larger program goes, I recommend you comment out these lines:

goal._tracer(0)
...
obstacle._tracer(0)

And your player turtle should show up. I suggest you not mess with tracer() until you've completed the bulk of your program and you understand what tracer() does.