RuntimeError：在 Timer 上设置 y 坐标时，主线程不在主循环中

Question

My son showed my some code he wrote in python ( he's learning through examples and is working on a basic block bouncing app).

He asked me to add "gravity" to his game so I added a 2 second timer that resets the y coordinate to 0 after pressing 'space'.

I get "main thread is not in main loop" error message when executing and I read some threads that explained that the timer I am using may not be on the right thread. I am not sure how to implement queueing and am wondering if there is an easier solution to this.

Thank you!

import turtle
from threading import Timer

wn = turtle.Screen()
wn.title("my game")
wn.bgcolor("blue")
wn.setup(width=1000, height=800)
wn.tracer(0)

#person
person = turtle.Turtle()
person.speed(0)
person.shape("square")
person.color("white")
person.shapesize(stretch_wid=1, stretch_len=1)
person.penup()
person.goto(-350, 0)

def personXX():
    x = person.xcor()
    x += 20
    person.setx(x)

def personXY():
    x = person.xcor()
    x -= 20
    person.setx(x)

def personYY():
    y = person.ycor()
    y += 20
    person.sety(y)

    r = Timer(2.0, fallToFloor )
  
    r.start()

def fallToFloor():
    y = person.ycor()
    y -= 20
    person.sety(y) 



    

wn.listen()
wn.onkeypress(personXY, "a")
wn.onkeypress(personXX, "d")
wn.onkeypress(personYY, "space")

while 1 == 1  :
    wn.update()

Answer 1

Using threading with turtle/tkinter is tricky as the graphics commands can only be invoked from the main thread. It can be done, but isn't really needed for this program as we can use turtle's own 'ontimer()` event to achieve the desired result:

from turtle import Screen, Turtle

def person_forward():
    person.forward(20)

def person_backward():
    person.backward(20)

def fallToFloor():
    person.sety(person.ycor() - 20)

def person_jump():
    person.sety(person.ycor() + 20)

    screen.ontimer(fallToFloor, 2000)  # milliseconds

screen = Screen()
screen.title("My Game")
screen.bgcolor('blue')
screen.setup(width=1000, height=800)

person = Turtle()
person.shape('square')
person.shapesize(stretch_wid=1, stretch_len=1)
person.color('white')
person.speed('fastest')
person.penup()
person.setx(-350)

screen.onkeypress(person_forward, 'd')
screen.onkeypress(person_backward, 'a')
screen.onkeypress(person_jump, 'space')
screen.listen()

screen.mainloop()