Handy Python stopwatch recipe for recording the time it takes to perform a task.

stopwatch.py

# Stopwatch recipe taken from Python Cookbook, 3rd Edition, by David Beazley and Brian K. Jones.
# Page 561: "As a general rule of thumb, the accuracy of timing measurements made with functions
# such as time.time() or time.clock() varies according to the operation system. In contast,
# time.perf_counter() always uses the highest-resolution timer available on the system."

import time

class Timer:
    def __init__(self, func=time.perf_counter):
        self.elapsed = 0.0
        self._func = func
        self._start = None

    def start(self):
        if self._start is not None:
            raise RuntimeError("Already started")
        self._start = self._func()

    def stop(self):
        if self._start is None:
            raise RuntimeError("Not started")
        end = self._func()
        self.elapsed += end - self._start
        self._start = None

    def reset(self):
        self.elapsed = 0.0

    @property
    def running(self):
        return self._start is not None

    def __enter__(self):
        self.start()
        return self

    def __exit__(self, *args):
        self.stop()