from tkinter import *


def mousepress(event):
    global pressX
    global pressY
    pressX = event.x
    pressY = event.y
    canvas.create_oval(event.x-3, event.y-3, event.x+3, event.y+3, fill="green")
    canvas.update()

def mouserelease(event):
    x = event.x
    y = event.y
    canvas.create_oval(x-3, y-3, x+3, y+3, fill="red")
    canvas.create_line(pressX, pressY, x, y, fill="blue")
    canvas.update()


def setup() :
    global window
    global canvas
    window = Tk()
    canvas = Canvas(window, width=450, height=300, bg = 'white')
    canvas.bind("<Button-1>", mousepress)
    canvas.bind("<ButtonRelease-1>", mouserelease)
    canvas.pack()
    window.mainloop()
 
setup()