Beep after long code cell execution in Jupyter Python

beeper.py

from time import time
from IPython import get_ipython
from IPython.display import Audio, display

class Beeper:

    def __init__(self, threshold, **audio_kwargs):
        self.threshold = threshold
        self.start_time = None    # time in sec, or None
        self.audio = audio_kwargs

    def pre_execute(self):
        if not self.start_time:
            self.start_time = time()

    def post_execute(self):
        end_time = time()
        if self.start_time and end_time - self.start_time > self.threshold:
            audio = Audio(**self.audio, autoplay=True)
            display(audio)
        self.start_time = None

beeper = Beeper(5, filename='beep-07.wav')

ipython = get_ipython()
ipython.events.register('pre_execute', beeper.pre_execute)
ipython.events.register('post_execute', beeper.post_execute)