My simple timer

timer.py

import time


class Timer:
    _events = []

    def _add_event(self):
        """Add a event time recode"""
        self._events.append(time.perf_counter())

    def start(self):
        """Starts the timer"""
        if not self.isRunning:
            self._add_event()

    def stop(self):
        """Stops (or pauses) the timer"""
        if self.isRunning:
            self._add_event()

    def reset(self):
        """Resets the timer"""
        self._events = []

    @property
    def isRunning(self):
        return bool(len(self._events) % 2)

    @property
    def lap_time(self):
        if self.isRunning:
            return time.perf_counter() - self._events[-1]
        return 0

    @property
    def elapsed(self):
        """Calculate total amount of elapsed time"""
        closed_lap = sum(e - b for b, e in zip(self._events[::2], self._events[1::2]))
        return closed_lap + self.lap_time


if __name__ == '__main__':
    t = Timer()
    t.start()
    time.sleep(0.5)
    t.stop()
    time.sleep(0.5)
    t.start()
    time.sleep(0.5)
    print(t.elapsed)

    time.sleep(1)
    t.stop()

    from datetime import timedelta
    print(str(timedelta(seconds=t.elapsed)))