[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:


New changeset 32318930da70ff03320ec50813b843e7db6fbc2e by Alexander Belopolsky 
(Mario Corchero) in branch 'master':
Closes bpo-31800: Support for colon when parsing time offsets (#4015)
https://github.com/python/cpython/commit/32318930da70ff03320ec50813b843e7db6fbc2e


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stage: patch review -> resolved
status: open -> closed

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

Note that #5288 relaxed the whole number of minutes restriction on UTC offsets. 
 Since the goal is to be able to parse the output of .isoformat(), I think %z 
should accept sub-minute offsets.

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Mario Corchero]

Mario Corchero  added the comment:

I have a patch to add 'Z' support as well if we are interested in making it the 
same as it glibc does. (as it supports it as well)

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Mario Corchero]

Mario Corchero  added the comment:

As a note

Seems support for the ":" was added in 2015 for glibc:
http://code.metager.de/source/xref/gnu/glibc/time/strptime_l.c#765

Commit e952e1df

Before that, it basically just ignores the minutes.

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Paul G]

Paul G  added the comment:

This seems very useful to me. I very frequently advise people *against* using 
dateutil.parser (despite my conflict of interest as maintainer of dateutil) for 
well-known formats, but the problem frequently comes up of, "what should I do 
when I have date created by isoformat()?", to which there's no clean satisfying 
answer other than, "use dateutil.parser even though you know the format."

I think the strptime page that Mario linked to is evidence that the %z 
directive is *intended* to match against -HH:MM, and so that might be the most 
"standard" solution.

That said, I somewhat prefer the granularity of the GNU date extensions %z, %:z 
and %::z, since this allows downstream users to be stricter about what they are 
willing to accept. I think either approach is defensible, but that *something* 
should be done soon, preferably for the 3.7 release.

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Mario Corchero]

Mario Corchero  added the comment:

Yep, http://man7.org/linux/man-pages/man3/strptime.3.html does support it even 
if it might look asymetrical.

Example:

   struct tm tm;
   char buf[255];

   memset(, 0, sizeof(struct tm));
   strptime("+00:00", "%z", );
   strftime(buf, sizeof(buf), "%z", );
   puts(buf); // Will print +
   exit(EXIT_SUCCESS);

Martin do you want me to "cleanup" the PR, add docs, news entry, etc?

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Martin Panter]

Martin Panter  added the comment:

FWIW it looks like “strptime” in glibc, and Open and Free BSD support parsing 
this and even more formats (RFC 822 and RFC 3339; includes “Z”, U.S. time 
zones, ±HH). Also, there is Issue 24954 for adding “%:z” like Gnu “date”.

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Martin Panter]

Martin Panter  added the comment:

Sorry, I meant Net BSD not Free BSD

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Mario Corchero]

Change by Mario Corchero :


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keywords: +patch
pull_requests: +3989
stage:  -> patch review

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[issue31800] datetime.strptime: Support for parsing offsets with a colon

[Mario Corchero]

New submission from Mario Corchero :

Currently, datetime.strptime does not support parsing utc offsets that include 
a colon. "+" is parsed without issues whilst it fails with "+00:00".

"+NN:NN" is not only ISO8601 valid but also the way the offset is presented to 
the user when using .isoformat on a datetime with a timezone/offset.

This lead to the users needing to go to external libraries like dateutil or 
iso8601 just to be able to parse the datetime encoded in strings that 
"datetime" produces.

Even if a long-term goal would be to provide a way to parse any isoformatted 
string this issue just aims to address the problem that the %z parsing 
presents. This already unblocks users from parsing datetime object serialized 
with isoformat.

With this change, the following will just work:

>>> import datetime as dt
>>> iso_fmt = '%Y-%m-%dT%H:%M:%S%z'
>>> d = dt.datetime.strptime('2004-01-01T10:10:10+05:00', iso_fmt)

*'2004-01-01T10:10:10+05:00' is a sample string generated via 
datetime.isoformat()

Other options like having a new %:z was proposed but having just %z seems much 
simpler for the user.



Note: There has been already conversations about adding support on datetime to 
parse any ISO-formatted string. This is a more simplistic approach. We might be 
able to get to that situation after this patch, but this aims just to unblock 
us.

Related:
http://www.loc.gov/standards/datetime/iso-tc154-wg5_n0039_iso_wd_8601-2_2016-02-16.pdf
https://mail.python.org/pipermail/python-ideas/2014-March/027018.html
https://bugs.python.org/issue15873

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components: Library (Lib)
messages: 304486
nosy: mariocj89
priority: normal
severity: normal
status: open
title: datetime.strptime: Support for parsing offsets with a colon
type: enhancement
versions: Python 3.7

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