tkinter 鼠标滚轮控制滚动条滚动

def processWheel(event):
    global vbar, canvas, step
    if event.delta > 0:
            # 滚轮往上滚动，放大
            canvas.yview_scroll(step, 'units')
    else:
            canvas.yview_scroll(step, 'units')
            # 滚轮往下滚动，缩小


canvas.bind("<MouseWheel>", processWheel)