classification
Title: datetime.fromtimestamp(t) when 0 <= t <= 86399 fails on Python 3.6
Type: behavior Stage: needs patch
Components: Windows Versions: Python 3.6
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: SilentGhost, ammar2, belopolsky, haypo, paul.moore, pekka.klarck, r.david.murray, steve.dower, tim.golden, tim.peters, zach.ware
Priority: normal Keywords: patch

Created on 2016-12-28 20:49 by pekka.klarck, last changed 2017-06-24 23:03 by ammar2.

Files
File name Uploaded Description Edit
forego_fold_detection.patch ammar2, 2016-12-30 11:08 review
truncate_negatives.patch ammar2, 2016-12-30 11:08 review
Pull Requests
URL Status Linked Edit
PR 2385 open ammar2, 2017-06-24 23:02
Messages (12)
msg284199 - (view) Author: Pekka Klärck (pekka.klarck) Date: 2016-12-28 20:49
For example:

E:\>py -3.6 -c "import datetime; datetime.datetime.fromtimestamp(42)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OSError: [Errno 22] Invalid argument

Works fine at least with Python 2.6-2.7 and 3.3-3.5. Only tested on Windows (missing deadsnakes for easy Linux testing).

I was also surprised to get OSError in general, but apparently fromtimestamp uses that instead of ValueError nowadays in some error situations.
msg284250 - (view) Author: SilentGhost (SilentGhost) * Date: 2016-12-29 12:08
This doesn't seem likely that it's anything to do with datetime, could you try reproducing it in repl?
msg284264 - (view) Author: Ammar Askar (ammar2) * Date: 2016-12-29 14:15
Can recreate successfully on windows, but not on linux:

> C:\Python36\python.exe -c "import datetime; datetime.datetime.fromtimestamp(42)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OSError: [Errno 22] Invalid argument

> C:\Python36\python.exe
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime; datetime.datetime.fromtimestamp(42)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument
msg284265 - (view) Author: SilentGhost (SilentGhost) * Date: 2016-12-29 14:35
Cannot reproduce this with the tip on linux
msg284269 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2016-12-29 14:52
Sounds like it really is an OSError (that is, that the Windows OS is the source of the error).  Whether or not we can or should do something about that is a separate question, though.
msg284272 - (view) Author: Ammar Askar (ammar2) * Date: 2016-12-29 15:28
The 86,399 upperbound comes from this line (max_fold_seconds=86400):

https://github.com/python/cpython/blob/master/Modules/_datetimemodule.c#L4277-L4278

The bug is introduced as part of the fold detection in this commit: https://github.com/python/cpython/commit/56376cacd2a0f6af834fe4d2a20b1a1095afb26f

Window's locatime_s function gives an EINVAL error when time is less than 0. Which is where the OSError comes from.

https://msdn.microsoft.com/en-us/library/a442x3ye.aspx
msg284281 - (view) Author: Ammar Askar (ammar2) * Date: 2016-12-29 17:00
I just ran the following script to check if there are any folds from timestamps [0, 86399] in any timezone.

  import datetime
  import pytz

  for tz in pytz.all_timezones:
      tz = pytz.timezone(tz)
      for i in range(86400):
          if datetime.datetime.fromtimestamp(i, tz).fold == 1:
              print(str(tz)) 

and it turns out there aren't any. I highly doubt any timezone is going to retroactively enable/disable DST during the epoch, so a potentially hacky fix is to just have a windows specific check for this value range.

I'm adding the people involved in PEP 495 to the nosy list so they can give their input.
msg284286 - (view) Author: Alexander Belopolsky (belopolsky) * (Python committer) Date: 2016-12-29 18:11
I think we should just clip the negative lower probe value to 0 on Windows before passing it to local().  Also, if we still care about platforms with 32-bit time_t, we should check for over/under flow *before* calling local().
msg284326 - (view) Author: Ammar Askar (ammar2) * Date: 2016-12-30 11:08
I've attached two patches that fix this behavior, one by simply foregoing the fold detection for this time range on windows (the patch that I'd argue is simpler and more readable)

And one that truncates the passed values to local to not be negative. This one would have been simple but unfortunately there's the complication that there are two local calls and additionally, the second one cannot be truncated to exactly 0 because then we incorrectly detect a fold for the timestamp 0.
msg296214 - (view) Author: Alexander Belopolsky (belopolsky) * (Python committer) Date: 2017-06-16 17:26
> I just ran the following script to check if there are any folds from timestamps [0, 86399] in any timezone.

Ammar, I am not sure pytz timezones support PEP 495 conventions. Can you repeat your experiment using the latest dateutil.tz or test.datetimetester.ZoneInfo from Python 3.6 test suit?

See <http://dateutil.readthedocs.io/en/stable/tz.html>.
msg296759 - (view) Author: Ammar Askar (ammar2) * Date: 2017-06-24 08:38
Hey, sorry for the late response. I just ran:

  import datetime
  from dateutil.zoneinfo import get_zonefile_instance
  import dateutil.tz

  zonenames = list(get_zonefile_instance().zones)

  for tz in zonenames:
      tz = dateutil.tz.gettz(tz)
      for i in range(86400):
          if datetime.datetime.fromtimestamp(i, tz).fold == 1:
              print(str(tz))

tz uses your OS's zone info so also posting my distro version:
Debian 8.8 - 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2 (2017-04-30) x86_64 GNU/Linux

And I got the same result, no timezone with folds in these range.
msg296795 - (view) Author: Ammar Askar (ammar2) * Date: 2017-06-24 23:03
Created a github pull request for the recommended patch along with a test: https://github.com/python/cpython/pull/2385
History
Date User Action Args
2017-06-24 23:03:14ammar2setmessages: + msg296795
2017-06-24 23:02:35ammar2setpull_requests: + pull_request2434
2017-06-24 08:38:09ammar2setmessages: + msg296759
2017-06-16 17:26:21belopolskysetmessages: + msg296214
2017-06-16 17:06:14r.david.murraylinkissue30684 superseder
2017-01-03 12:52:38hayposetnosy: + haypo
2016-12-30 11:08:56ammar2setfiles: + truncate_negatives.patch
2016-12-30 11:08:44ammar2setfiles: + forego_fold_detection.patch
keywords: + patch
messages: + msg284326
2016-12-29 18:11:00belopolskysetmessages: + msg284286
2016-12-29 17:00:53ammar2setnosy: + tim.peters
messages: + msg284281
2016-12-29 15:28:04ammar2setmessages: + msg284272
2016-12-29 14:52:39r.david.murraysetnosy: + r.david.murray
messages: + msg284269
2016-12-29 14:35:22SilentGhostsetmessages: + msg284265
2016-12-29 14:34:03SilentGhostsetnosy: + belopolsky, paul.moore, tim.golden, zach.ware, steve.dower

type: behavior
components: + Windows
stage: needs patch
2016-12-29 14:15:05ammar2setnosy: + ammar2
messages: + msg284264
2016-12-29 12:08:25SilentGhostsetnosy: + SilentGhost
messages: + msg284250
2016-12-28 20:49:20pekka.klarckcreate