from tkinter import *
import webbrowser

root = Tk()

w = Canvas(root,width=400,height=200)

w.pack()

def paint(event):
    x1,y1 = (event.x-1),(event.y-1)
    x2,y2 = (event.x+1),(event.y+1)
    w.create_oval(x1,y1,x2,y2,fill="red")
w.bind("<B1-Motion>",paint)

Label(root,text="使用鼠标左键开始画图").pack(side=BOTTOM)
mainloop()