Steven D'Aprano added the comment: On 04/08/13 05:31, Alexander Belopolsky wrote: > > Alexander Belopolsky added the comment: > > Here is the use-case that was presented to support adding additional > operations on timedelta objects: > > """ > I'm conducting a series of observation experiments where I > measure the duration of an event. I then want to do various > statistical analysis such as computing the mean, median, > etc. Originally, I tried using standard functions such as > lmean from the stats.py package. However, these sorts of > functions divide by a float at the end, causing them to fail > on timedelta objects. Thus, I have to either write my own > special functions, or convert the timedelta objects to > integers first (then convert them back afterwards). > """ (Daniel Stutzbach, in msg26267 on issue1289118.) > > The proposed statistics module does not support this use case: [...] > TypeError: sum only accepts numbers
That's a nice use-case, but I'm not sure how to solve it, or whether it needs to be. I'm not going to add support for timedelta objects as a special-case. Once we start special-casing types, where will it end? At first I thought that registering timedelta as a numeric type would help, but that is a slightly dubious thing to do since timedelta doesn't support all numeric operations: py> datetime.timedelta(1, 1, 1)+2 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'datetime.timedelta' and 'int' (What would that mean, anyway? Add two days, two seconds, or two milliseconds?) Perhaps timedelta objects should be enhanced to be (Integral?) numbers. In the meantime, there's a simple way to do this: py> from datetime import timedelta as td py> data = [td(2), td(1), td(3), td(4)] py> m = statistics.mean([x.total_seconds() for x in data]) py> m 216000.0 py> td(seconds=m) datetime.timedelta(2, 43200) And for standard deviation: py> s = statistics.stdev([x.total_seconds() for x in data]) py> td(seconds=s) datetime.timedelta(1, 25141, 920371) median works without any wrapper: py> statistics.median(data) datetime.timedelta(2, 43200) I'm now leaning towards "will not fix" for supporting timedelta objects. If they become proper numbers, then they should just work, and if they don't, supporting them just requires a tiny bit of extra code. However, I will add documentation and tests for them. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue18606> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
