TypeError：异常必须派生自BaseException

Question

我也在该站点上看到了这段代码，我想在我的项目中实现它之前尝试一下这些代码。但是似乎我很难理解baseException，因为我在python中不太好。这是代码：

from threading import Timer
import time
import sys

class Watchdog:
    def __init__(self, timeout, userHandler=None):  # timeout in seconds
        self.timeout = timeout
        self.handler = userHandler if userHandler is not None else self.defaultHandler
        self.timer = Timer(self.timeout, self.handler)
        self.timer.start()


    def reset(self):
        self.timer.cancel()
        self.timer = Timer(self.timeout, self.handler)
        self.timer.start()


    def stop(self):
        self.timer.cancel()


    def defaultHandler(self):
        raise self

watchdog = Watchdog(5)
count = 0
while(count < 4):
    try:
      count = count + 1
      print(count)
      time.sleep(1)
    except Watchdog:
      print("I'm a fancy error message")
watchdog.stop()

然后我收到此错误消息：

    Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.5/threading.py", line 1180, in run
    self.function(*self.args, **self.kwargs)
  File "/home/pi/wdt.py", line 24, in defaultHandler
    raise self
TypeError: exceptions must derive from BaseException

我不知道该如何解决这个问题。我在互联网上进行了大量搜索，但没有找到解决方案。请帮我解决这个问题。谢谢。