Python tkinter 画布动画

Question

so i was writing this code and when i run it my animated ball is going only right side but not turning back can you help me

import tkinter
canvas = tkinter.Canvas(bg="white",width=(900),height=(900))
canvas.pack()


def ball():
    global x
    canvas.delete("all")
    canvas.create_oval(x-100,y-100,x+100,y+100,fill="orange",outline="black",width=4)
    x = x+5
    if x <800:
        canvas.after(20,ball)

def ball_back():
    global x
    canvas.delete("all")
    canvas.create_oval(x-100,y-100,x+100,y+100,fill="orange",outline="black",width=4)
    x = x-5
    if x >100:
        canvas.after(20,ball_back)

x = 100
y = 300
ball()
ball_back()

Answer 1

The way Tkinter calls those methods is a little different than what you may expect. Both ball and ball_back are being called right away one after another. Since ball_back fails the if statement right out of the gate (x is greater than 100) it never gets called again. Try changing the last lines of ball to this:

x = x+5
if x <800:
    canvas.after(20,ball)
else:
    canvas.after(20, ball_back)