Movatterモバイル変換
[0]ホーム
[Python-Dev] Proposing an alternative to PEP 410
Larry Hastingslarry at hastings.org
Thu Feb 23 22:28:14 CET 2012
I've been meditating on the whole os.stat mtime representation thing.Here's a possible alternative approach.* Improve datetime.datetime objects so they support nanosecond resolution, in such a way that it's 100% painless to make them even more precise in the future.* Add support to datetime objects that allows adding and subtracting ints and floats as seconds. This behavior is controllable with a flag on the object--by default this behavior is off.* Support accepting naive datetime.datetime objects in all functions that accept a timestamp in os (utime etc).* Change the result of os.stat to be a custom class rather than a PyStructSequence. Support the sequence protocol on the custom class but mark it PendingDeprecation, to be removed completely in 3.5. (I can't take credit for this idea; MvL suggested it to me once while we were talking about this issue. Now that the os.stat object has named fields, who uses the struct unpacking anymore?)* Add support for setting "stat_float_times=2" (or perhaps "stat_float_times=datetime.datetime" ?) to enable returning st_[acm]time as naive datetime.datetime objects--specifically, ones that allow addition and subtraction of ints and floats. The value would be similar to calling datetime.datetime.fromdatetime() on the current float timestamp, but would preserve all available precision.* Add a new parameter to functions that produce stat-like timestamps to explicitly specify the type of the timestamps (float or datetime), as proposed in PEP 410.I realize datetime objects aren't a drop-in replacement for floats (or ints).In particular their str/repr representations are much more ornate. So I'dexpect some breakage.Personally I think the adding/subtracting ints change is a tiny bitsmelly--but this is a practicality beating purity thing. I propose makingit non-default behavior just to minimize the effects of the change.Similarly, I realize os.stat_float_times was always a bit of a hack, whatwith it being global state and all. However the approach has the virtue ofhaving worked in the past.I disagree with PEP 410's conclusions about the suitability of datetime asa timestamp object. I think "naive" datetime objects are a perfect fit.Specficially addressing PEP 410's concerns: * I don't propose doing anything about the other functions that have no explicit start time; I'm only proposing changing the functions that deal with timestamps. (Perhaps the right thing for epoch-less times like time.clock would be timedelta? But I think we can table this discussion for now.) * "You can't compare naive and non-naive datetimes." So what? The existing timestamp from os.stat is a float, and you can't compare floats and non-naive datetimes. How is this an issue?Perhaps someone else can propose something even better,//arry/
More information about the Python-Devmailing list
[8]ページ先頭