timer.py

# timer.py


import time


class TimerError(Exception):

    """A custom exception used to report errors in use of Timer class"""


class Timer:

    def __init__(self):

        self._start_time = None


    def start(self):

        """Start a new timer"""

        if self._start_time is not None:

            raise TimerError(f"Timer is running. Use .stop() to stop it")


        self._start_time = time.perf_counter()


    def stop(self):

        """Stop the timer, and report the elapsed time"""

        if self._start_time is None:

            raise TimerError(f"Timer is not running. Use .start() to start it")


        elapsed_time = time.perf_counter() - self._start_time

        self._start_time = None

        print(f"Elapsed time: {elapsed_time:0.8f} seconds")