Python timer class

timer.py

# timer.py
"""
Usage:
>>> from timer import Timer
>>> t = Timer() ## or for logger:  t = Timer(logger=logger.info)
>>> t.start()

>>> t.stop()  # A few seconds later
Elapsed time: 3.8191 seconds
"""
import time

class TimerError(Exception):
    """A custom exception used to report errors in use of Timer class"""

class Timer:
    def __init__(self, text="Elapsed time: {:0.4f} seconds", logger=print):
        """
        Init

        Args:
            text (str, optional): Text format. Defaults to "Elapsed time: {:0.4f} seconds".
            logger (logger type, optional): Either print or logger.info function. Defaults to print.
        """
        self._start_time = None
        self.text = text
        self.logger = logger

    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

        if self.logger:
            self.logger(self.text.format(elapsed_time))

        return elapsed_time