humanfriendly.Timer won't work properly if the system clock changes

[mwgamble]

If the system clock changes while the Timer class is busy timing something, it won't track the elapsed time correctly. This could happen if daylight saving kicks in, or if someone travels across a border and their timezone changes, or for any number of other reasons, such as a NTP client kicking in and changing the time. A great example of this can be found in this video by Tom Scott: https://www.youtube.com/watch?v=QCwpVtqcqNE

The solution is to use a monotonic clock to track the time. Fortunately, python has built-in support for monotonic clocks: https://docs.python.org/3/library/time.html?highlight=time.monotonic#time.monotonic
There is also a polyfill available for when time.monotonic isn't available: https://pypi.python.org/pypi/monotonic

It would be great if Timer could be adjusted to use a monotonic clock so that it can properly track the elapsed time regardless of its conditions of use.

[xolox]

Hi Matthew and thanks for the feedback! I was aware of time.monotonic() being available in Python 3.3 and higher, but I'd never encountered pypi.python.org/pypi/monotonic before. There's actually a sense of elegance to the monotonic package, in that it doesn't require compilation (binary code) and it's contained in a single Python module. I like!

Just now I released humanfriendly 2.3 which uses monotonic timers when available, whether via the new conditional monotonic dependency or time.monotonic(). If no monotonic clock is available it falls back to time.time(), but now only as a last resort :-).

I believe this resolves the problem you reported so I'm going to close this issue now. If you notice anything wrong, feel free to reopen this issue or open a new one.