Regression: test_datetime fails on 3.5, Win 7, works on 3.4

[terryjreedy]

BPO	25092
Nosy	@terryjreedy, @abalkin, @vstinner, @ericvsmith, @bitdancer, @skrah, @zware, @eryksun, @zooba
Files	25092_1.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = 'https://github.com/zooba'
closed_at = <Date 2015-09-23.01:23:44.666>
created_at = <Date 2015-09-14.02:54:18.671>
labels = ['type-bug', 'library']
title = 'Regression: test_datetime fails on 3.5, Win 7, works on 3.4'
updated_at = <Date 2015-09-23.01:23:44.665>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2015-09-23.01:23:44.665>
actor = 'steve.dower'
assignee = 'steve.dower'
closed = True
closed_date = <Date 2015-09-23.01:23:44.666>
closer = 'steve.dower'
components = ['Library (Lib)']
creation = <Date 2015-09-14.02:54:18.671>
creator = 'terry.reedy'
dependencies = []
files = ['40469']
hgrepos = []
issue_num = 25092
keywords = ['patch', '3.5regression']
message_count = 25.0
messages = ['250600', '250607', '250616', '250623', '250659', '250660', '250662', '250666', '250671', '250673', '250674', '250676', '250677', '250678', '250679', '250680', '250682', '250683', '250708', '250709', '250710', '250714', '250742', '251350', '251365']
nosy_count = 12.0
nosy_names = ['terry.reedy', 'belopolsky', 'vstinner', 'eric.smith', 'r.david.murray', 'skrah', 'python-dev', 'zach.ware', 'eryksun', 'steve.dower', 'JohnLeitch', 'brycedarling']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25092'
versions = ['Python 3.5']

[terryjreedy]

PS C:\Users\Terry> py -3 -m test test_datetime
[1/1] test_datetime
test test_datetime failed -- Traceback (most recent call last):
  File "C:\Programs\Python 3.5\lib\test\datetimetester.py", line 1154, in test_strftime
    self.assertEqual(t.strftime(""), "") # SF bug python/cpython#38716
ValueError: Invalid format string

Same result 3 times.

[abalkin]

Looks like something related to bpo-24917.

[zware]

I can reproduce. I'm bewildered as to why none of the buildbots are complaining about this.

[zware]

Interestingly, the re-run performed by regrtest's '-w' flag did not fail.

[zooba]

Maybe errno needs to be explicitly cleared before calling strftime or else we're seeing someone else's EINVAL?

[zooba]

(In the C code I mean, not in the test.)

[skrah]

Yes, errno should always be cleared before use (in C99 at least,
not sure what the crt does).

[eryksun]

errno should always be cleared before use (in C99 at least,
not sure what the crt does).

The CRT's strftime doesn't clear errno. I suggested clearing it in bpo-25029, msg250215.

[zooba]

I guess when I said I'd done "exactly" what you suggested I misread that part... whoops.

This is a pretty nasty bug to workaround... do we have any way for a user to clear errno from their own code?

[skrah]

Clearing is easy: errno = 0; :)

C library functions are not supposed to set errno to 0 by
themselves (C99: paragraph 7.5).

[zooba]

I get that part.

Is there a way people can set errno to zero from Python code? Or do we need to ship 3.5.1 already?

[vstinner]

It's common in Modules/posixmodule.c to set errno to 0 before calling a C function, especially when "errno != 0" is checked after the call (because it's the only way to check if the function failed?).

[bitdancer]

Given all the changes in the windows support in 3.5, I will not be at all surprised if we need to spin 3.5.1 much more quickly than we normally would in any case.