如何实现tkinter的after方法？

Question

程序从tkinter导入中读取systemRunTime和systemFrequency。

如果不为0，则想以systemFrequency速率执行publish_message，以秒为单位。systemRunTime确定以systemFrequency对象确定的速率执行publish_message命令的次数。

尝试使用睡眠，但不适用于tkinter导入。

当前正在获取AttributeError：'NoneType'对象没有属性'after。

 def __init__(self, master=None):
    self.master = master
    self.pubnmonitor = tk.Tk()
    ...

def send_message(self):
    systemFrequency = float(freqSettings.systemFrequency)
    systemRunTime = int(freqSettings.systemRunTime)
    global count
    count = 0

    if systemFrequency == 0:
        while (count < systemRunTime):
             self.publish_message()
             count +=1
    else:
        self.schedule()

def schedule(self):
    global count
    if count >= systemRunTime:
        return
    self.publish_message()
    count+=1
    self.master.after(1000*systemFrequency, schedule, self)