maximum recursion depth exceeded

[Gribouillis]

A good principle is to avoid time.sleep() with GUIs because it freezes the GUI. You can use tkinter's after() method. Something like

startClickingVar = False

def click_forever():
    if startClickingVar:
        mouse.click(Button.left, 1)
        root.after(1000, click_forever)

def startClick():
    global startClickingVar
    if not startClickingVar:
        startClickingVar = True
        click_forever()

def stopClick():
    global startClickingVar
    startClickingVar = False