[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Change by Alexander Belopolsky :


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status: open -> closed

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:


New changeset 0e06be836ca0d578cf9fc0c68979eb682c00f89c by Alexander Belopolsky 
(Miss Islington (bot)) in branch '3.7':
Add What's new entry for datetime.fromisoformat (GH-5559) (GH-5939)
https://github.com/python/cpython/commit/0e06be836ca0d578cf9fc0c68979eb682c00f89c


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[miss-islington]

Change by miss-islington :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:


New changeset 22864bc8e4a076bbac748ccda6c27f1ec41b53e7 by Alexander Belopolsky 
(Paul Ganssle) in branch 'master':
Add What's new entry for datetime.fromisoformat (#5559)
https://github.com/python/cpython/commit/22864bc8e4a076bbac748ccda6c27f1ec41b53e7


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Change by Paul Ganssle :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Change by Paul Ganssle :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[R. David Murray]

R. David Murray  added the comment:

Correct, a new feature should always get a what's new entry.  You could submit 
a PR for it :)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy  added the comment:

maybe it's worth adding an entry in python 3.7 "what's new" ? I think it was a 
very long awaited issue.
The opposite of isoformat() is a very frequent question from python newcomers

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:


New changeset 09dc2f508c8513e0466a759cc27a09108c1e55c2 by Alexander Belopolsky 
(Paul Ganssle) in branch 'master':
bpo-15873: Implement [date][time].fromisoformat (#4699)
https://github.com/python/cpython/commit/09dc2f508c8513e0466a759cc27a09108c1e55c2


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Daniel Holmes]

Daniel Holmes  added the comment:

I wanted to note here... I've been trying to get strptime to work with the 
types of dates specified in this request and came across a documentation bug 
here: https://docs.python.org/3.5/library/time.html#time.strptime

You can see that the %z attribute's examples given have colons in them while 
the format specified is +HHMM rather than +HH:MM which the examples illude to.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Paul Ganssle  added the comment:

> Not if the time is associated with a particular day. Imagine implementing 
> datetime.fromisoformat by separately calling date.fromisoformat and 
> time.fromisoformat. The date will be off by one day if you naively rounded 
> 2017-12-18 23:59 “up” to 2017-12-18 00:00.

Yes, I suppose this is a problem if you implement it that way. Seems like a 
somewhat moot point, but I think any decision about rounding should probably be 
driven by what people are expecting more than by how it is implemented.

That said, I can see a good case for truncation *and* rounding up for something 
like '2016-12-31T23:59:59.9'. Rounding up to '2017-01-01' is certainly 
the closest whole millisecond to round to, *but* often people expressing a 
"23:59:59.999" are trying to actually express "the last possible moment 
*before* 00:00".

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter  added the comment:

Not if the time is associated with a particular day. Imagine implementing 
datetime.fromisoformat by separately calling date.fromisoformat and 
time.fromisoformat. The date will be off by one day if you naively rounded 
2017-12-18 23:59 “up” to 2017-12-18 00:00.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Paul Ganssle  added the comment:

@martin.panter I don't see the problem here? Wouldn't 23:59.995 round up to 
00:00?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter  added the comment:

Regarding Matthieu’s RFC 3339 parser, Victor wanted to use the 
round-half-to-even rule to get a whole number of microseconds. But considering 
the “time” class cannot represent 24:00, how do you round up in the extreme 
case past 23:59?

time.fromisoformat("23:59:59.995")

Perhaps it is better to always truncate to zero, only support 6 digits 
(rejecting fractions of a microsecond), or add Anders’s 
truncate_microseconds=True option.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy  added the comment:

I finally released my work. It looks like Paul's work is more comprehensive, 
but if you want to pick one thing or two in mine, feel free.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Roundup Robot]

Change by Roundup Robot :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Paul Ganssle  added the comment:

> The other difference is Mattieu guarantees ValueError for invalid input 
> strings, which I think is good.

I forgot to address this - but I don't think this is a difference in 
approaches. If you pass `None` or an int or something, the problem is with the 
type, not the value, so at a minimum you're looking at TypeError and ValueError 
- and those are the only exceptions raised in my patch.

(I'll note that my patch does not accept bytes, though this is something of an 
artificial limitation, since the patch makes use of the fact that all valid 
isoformat() strings will contain at most exactly 1 non-ascii character in 
position 10, so we could easily work around this, but I think the trend for 
CPython is to avoid blurring the lines between bytes and str rather than 
encouraging their interchangeable use.)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

+1 on what Paul said.

Mathieu, the goal for 3.7 will be to get Paul's PR merged.  It will be great if 
you could help in reviewing it.  We can return to the features in your PR 
during the 3.8 development cycle.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Paul Ganssle  added the comment:

> The better is the enemy of the good here.  Given the history of this issue, I 
> would rather accept a well documented restrictive parser than wait for a more 
> general code to be written.  Note that we can always relax the parsing rules 
> in the future.

This is in fact the exact reason why I wrote the isoformat parser like I did, 
because ISO 8601 is actually a quite expansive standard, and this is the least 
controversial subset of the features. In fact, I spent quite a bit of time on 
adapting the general purpose ISO8601 parser I wrote for dateutil *into* one 
that only accepts the output of isoformat() because it places a minimum burden 
on ongoing support, so it's not really a matter of waiting for a more general 
parser to be written.

I suggest that for Python 3.7 we *only* support output of isoformat(). Many 
general iso8601 parsers exist, including the one I have already implemented for 
python-dateutil (which will be part of the dateutil 2.7.0 release). We can have 
further discussion later about what exactly should be supported in Python 3.8, 
but even in the pre-release discussions I'm already seeing pushback about some 
of the more unusual 8601 formats, and it's a *lot* easier to explain (in 
documentation) that `fromisoformat()` is intended to be the inverse of 
`isoformat()` than it is to explain which variations of ISO 8601 are and are 
not supported (fractional minutes? if you're following the standard, the 
separator has to be a T, so what other variations of the standard are allowed?).

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy  added the comment:

I'm right now available again to work on this issue. I'll submit a pull
request within a week with all issues addressed

Le 4 déc. 2017 11:45 PM, "Alexander Belopolsky"  a
écrit :

>
> Alexander Belopolsky  added the comment:
>
> The better is the enemy of the good here.  Given the history of this
> issue, I would rather accept a well documented restrictive parser than wait
> for a more general code to be written.  Note that we can always relax the
> parsing rules in the future.
>
> --
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

The better is the enemy of the good here.  Given the history of this issue, I 
would rather accept a well documented restrictive parser than wait for a more 
general code to be written.  Note that we can always relax the parsing rules in 
the future.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter  added the comment:

The other difference is Mattieu guarantees ValueError for invalid input 
strings, which I think is good.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter  added the comment:

P-ganssle seems to be proposing to limit parsing to exactly what 
“datetime.isoformat” produces; i.e. whole number of seconds, milliseconds or 
microseconds. Personally I would prefer it without this limitation, like in 
Mathieu’s patches. But P-ganssle has done some documentation, so perhaps we can 
combine the work of each?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Ganssle]

Change by Paul Ganssle :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Elvis Pranskevichus]

Elvis Pranskevichus  added the comment:

I think that both the pyiso8601 and boxed/iso8601 implementations parse ISO 
8601 strings incorrectly.  The standard explicitly says that all truncated 
datetime strings are *reduced accuracy timestamps*.  In other words, "2017-10" 
is *not* equal to "2017-10-01".  Instead, "2017-10" represents the whole month 
of October 2017.  Same thing with hours.  Earlier versions of ISO 8601 even 
allowed dropping the year: "--10-01", which meant October 1st of _any year_.  
They dropped this from more recent revisions of the standard.

The only place where the truncated representation means "default to zero" is 
the timezone offset, so "10:10:00+4" and "10:10:00+04:00" mean the same thing.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Anders Hovmöller]

Anders Hovmöller added the comment:

@larsonreever That lib is pretty limited, in that it doesn't handle dates or 
deltas. Again: my lib that is linked above does and has comprehensive tests.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[larsonreever]

larsonreever added the comment:

Otherwise, py8601 (https://bitbucket.org/micktwomey/pyiso8601/) looks pretty 
popular and well maintained (various committers, started in 2012, last commit 
in 2016).  I don't think that we should add the iso8601 module to the stdlib, 
but merge iso8601 "features" into the datetime module.  The iso8601 module 
supports Python 2.7 and so has to implement its own timezone classes. The 
datetime module now has datetime.timezone since Python 3.2 for fixed timezone. 
To me it's the finest, the most elegant, and no other one can claim to be more 
robust since it's probably the #1 iso parsing functions used in python. Have a 
look at 
https://docs.djangoproject.com/en/1.9/_modules/django/utils/dateparse/#parse_datetime.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mantas Zimnickas]

Changes by Mantas Zimnickas :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Nick Coghlan]

Changes by Nick Coghlan :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Cherniavsky Beni]

Changes by Cherniavsky Beni :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

Please move _parse_isotime to _strptime so that it can be called from C 
implementation.  Also, the new method should be documented.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

updated version with SilentGhost's concerns addressed.

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Added file: http://bugs.python.org/file44019/fromisoformat_regexinclasses2.patch

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Changes by Mathieu Dupuy :


Added file: 
http://bugs.python.org/file44016/fromisoformat_strptimesingledispatch.patch

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Changes by Mathieu Dupuy :


Added file: http://bugs.python.org/file44015/fromisoformat_regexinclasses.patch

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

I'm back on the issue. I'm currently stuck on the design. We need to store the 
regexes somewhere, and that's what causes problem : I can't really find a good 
place to store them. We basically have two possible designs :
* single dispatch kind, class-type dictionary lookup for regexes, stored in 
_strpime.py. It's minimally invasive, allow a very simple C implementation, and 
allows us to avoid to add a 're' import in datetime.py. Problem : it breaks 
when the given class is not of type date, time or datetime. And it currently 
breaks the tests because tests are doing this, testing using subclasses. We 
could rely on "isinstance" but do we want this ?

* regex stored as classes attributes. More robust, more invasive, 're' import 
in datetime.py, allows subclassing, passes test. C implementation not done yet. 
Since it requires a better understanding of the C API, I will do it only we are 
sure that's the way to go.

I post the two versions of the implementation as patches here. These adress all 
the concerns expressed before (Martin). If we can't decide, I will post a mail 
on the mailing list Martin suggested, python-ideas. By the way, are you sure 
it's the right one to ask ? Wouldn't be python-dev more appropriated ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

Mathieu: Maybe you haven’t seen some of the comments on your older patches. 
E.g. my comment on fromisoformat4.patch about improper use of “with 
self.assertRaises(...)” still stands.

Also, adding some documentation to the patch might help the likes of Anders 
figure out the scope of the change. I think we decided to parse RFC 3339’s 
“internet date and time format” profile of ISO 8601 with the date, time, and 
datetime classes, including tolerating arbitrary resolutions of fractions of 
seconds in the time, and parsing time zones.

I don’t think we need to test every combination of the other ISO 8601 formats. 
There are already a couple of negative tests. Are there any in particular you 
think are important to add?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Anders Hovmöller]

Anders Hovmöller added the comment:

Hmm, ok. I guess I was confused by "dates and times" part of the subject. Ok, 
so only datetimes. My other comments still apply though. 

> On 19 Jul 2016, at 16:20, Mathieu Dupuy  wrote:
> 
> 
> Mathieu Dupuy added the comment:
> 
> because it limits itself to only support the RFC 3339 subset, as
> explained in the begining of the discussion.
> 
> 2016-07-19 16:07 GMT+02:00 Anders Hovmöller :
>> 
>> Anders Hovmöller added the comment:
>> 
>> The tests attached to this ticket seem pretty bare. Issues that I can spot 
>> directly:
>> 
>> - only tests for datetimes, not times or dates
>> - only tests for zulu and "-8:00” timezones
>> - no tests for invalid input (parsing a valid date as a datetime for example)
>> - only tests for -MM-DDTHH:MM:SSZ, but ISO8601 supports:
>>- Naive times
>>- Timezone information (specified as offsets or as Z for 0 offset)
>>- Year
>>- Year-month
>>- Year-month-date
>>- Year-week
>>- Year-week-weekday
>>- Year-ordinal day
>>- Hour
>>- Hour-minute
>>- Hour-minute
>>- Hour-minute-second
>>- Hour-minute-second-microsecond
>>- All combinations of the three "families" above!
>> (the above list is a copy paste from my project that implements all ISO8601 
>> that fits into native python: https://github.com/boxed/iso8601 
>> )
>> 
>> This is a more reasonable test suite: 
>> https://github.com/boxed/iso8601/blob/master/iso8601.py#L166 
>>  although it 
>> lacks the tests for bogus inputs.
>> 
>>> On 2016-07-16, at 03:41, Alexander Belopolsky  
>>> wrote:
>>> 
>>> 
>>> Alexander Belopolsky added the comment:
>>> 
>>> I would very much like to see this ready before the feature cut-off for 
>>> Python 3.6.  Could someone post a summary on python-ideas to get a show of 
>>> hands on some of the remaining wrinkles?
>>> 
>>> I would not worry about a C implementation at this point.  We can put 
>>> python implementation in _strptime.py and call it from C as we do for the 
>>> strptime method.
>>> 
>>> --
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

because it limits itself to only support the RFC 3339 subset, as
explained in the begining of the discussion.

2016-07-19 16:07 GMT+02:00 Anders Hovmöller :
>
> Anders Hovmöller added the comment:
>
> The tests attached to this ticket seem pretty bare. Issues that I can spot 
> directly:
>
> - only tests for datetimes, not times or dates
> - only tests for zulu and "-8:00” timezones
> - no tests for invalid input (parsing a valid date as a datetime for example)
> - only tests for -MM-DDTHH:MM:SSZ, but ISO8601 supports:
> - Naive times
> - Timezone information (specified as offsets or as Z for 0 offset)
> - Year
> - Year-month
> - Year-month-date
> - Year-week
> - Year-week-weekday
> - Year-ordinal day
> - Hour
> - Hour-minute
> - Hour-minute
> - Hour-minute-second
> - Hour-minute-second-microsecond
> - All combinations of the three "families" above!
> (the above list is a copy paste from my project that implements all ISO8601 
> that fits into native python: https://github.com/boxed/iso8601 
> )
>
> This is a more reasonable test suite: 
> https://github.com/boxed/iso8601/blob/master/iso8601.py#L166 
>  although it 
> lacks the tests for bogus inputs.
>
>> On 2016-07-16, at 03:41, Alexander Belopolsky  wrote:
>>
>>
>> Alexander Belopolsky added the comment:
>>
>> I would very much like to see this ready before the feature cut-off for 
>> Python 3.6.  Could someone post a summary on python-ideas to get a show of 
>> hands on some of the remaining wrinkles?
>>
>> I would not worry about a C implementation at this point.  We can put python 
>> implementation in _strptime.py and call it from C as we do for the strptime 
>> method.
>>
>> --
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Anders Hovmöller]

Anders Hovmöller added the comment:

The tests attached to this ticket seem pretty bare. Issues that I can spot 
directly:

- only tests for datetimes, not times or dates
- only tests for zulu and "-8:00” timezones
- no tests for invalid input (parsing a valid date as a datetime for example)
- only tests for -MM-DDTHH:MM:SSZ, but ISO8601 supports:
- Naive times
- Timezone information (specified as offsets or as Z for 0 offset)
- Year
- Year-month
- Year-month-date
- Year-week
- Year-week-weekday
- Year-ordinal day
- Hour
- Hour-minute
- Hour-minute
- Hour-minute-second
- Hour-minute-second-microsecond
- All combinations of the three "families" above!
(the above list is a copy paste from my project that implements all ISO8601 
that fits into native python: https://github.com/boxed/iso8601 
)

This is a more reasonable test suite: 
https://github.com/boxed/iso8601/blob/master/iso8601.py#L166 
 although it 
lacks the tests for bogus inputs.

> On 2016-07-16, at 03:41, Alexander Belopolsky  wrote:
> 
> 
> Alexander Belopolsky added the comment:
> 
> I would very much like to see this ready before the feature cut-off for 
> Python 3.6.  Could someone post a summary on python-ideas to get a show of 
> hands on some of the remaining wrinkles?
> 
> I would not worry about a C implementation at this point.  We can put python 
> implementation in _strptime.py and call it from C as we do for the strptime 
> method.
> 
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

I would very much like to see this ready before the feature cut-off for Python 
3.6.  Could someone post a summary on python-ideas to get a show of hands on 
some of the remaining wrinkles?

I would not worry about a C implementation at this point.  We can put python 
implementation in _strptime.py and call it from C as we do for the strptime 
method.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Anders Hovmöller]

Anders Hovmöller added the comment:

> 
> By the way, I just discovered, that the way we treat microseconds differs 
> from the strptime one : we are smarter read every digits and smartly round to 
> six, strptime doesn't go that far and just *truncate* to this. Should go that 
> way, for consistency with what strptime does, maybe ?

I'm strongly against silently throwing away data and calling it even. If we 
want compatibility with strptime then it should be a separate flag like 
silent_truncate_milliseconds=True. 

On another matter: does the latest proposed code pass the tests in my ISO8601 
implementation that I mentioned 2013 (! time flies)?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

Hi.
I'm back, and willing to move forward on this issue. With the new code layout, 
the compiled regexes  now lay in datetime classes as class attributes. Will it 
be possible to import date, time and datetime from datetime.py in _datetime.c 
without a problem ?

By the way, I just discovered, that the way we treat microseconds differs from 
the strptime one : we are smarter read every digits and smartly round to six, 
strptime doesn't go that far and just *truncate* to this. Should go that way, 
for consistency with what strptime does, maybe ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Eric Hanchrow]

Changes by Eric Hanchrow :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

If you decide to only do a Python implementation, the main reason to write a 
wrapper in C would be because the datetime class is defined in C. Similar to 
how the datetime_strptime() function in Modules/_datetimemodule.c imports and 
calls _strptime._strptime_datetime().

An alternative might be to subclass the C classes _datetime.datetime, etc, and 
define the methods directly in those subclasses. Similar to how the C-defined 
class _socket.socket is subclassed in Lib/socket.py and more methods are added.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

I know. Martin was suggesting to defer the processing to an actual Python 
implementation, hence my answer.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

> If I defer the actual processing to the Python part, what's the point of 
> doing a C part ?

Currently, the "datetime" module is fully implemented in C, it's the
_datetime module in practice (accessed by the datetime module
namespace).

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

What I really want is to use regex in the C part as I did for the python one. 
It's the best approach and by very far.
I need to figure out how to use regex in CPython internals.

If I defer the actual processing to the Python part, what's the point of doing 
a C part ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

Did you see my class attributes suggestion a couple messages back? That might 
solve your dispatch problem:

def _parse_isodatetime(cls, string):
match = cls._iso_regex.match(...)

class time:
_iso_regex = re.compile(...)

# or

time._iso_regex = re.compile(...)
date._iso_regex = ...

For the C module, start looking at /Modules/datetimemodule.c. Maybe if you can 
think of a similar function implemented in C to copy off. It looks like 
strptime() defers to a Python-only implementation; maybe that is another option.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[SilentGhost]

SilentGhost added the comment:

Probably only other solution that I see is to add the third argument, an actual 
class, e.g.:

_parse_isodatetime(cls, string, datetime)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

crap, here is the attachment.
Yeah, but I really would like to use regex in the C version (unless you 
strongly disadvise), so we will have the same logic and the same problem. And I 
never made a patch for the C interpreter itself, so the C equivalent is not 
close to be here soon. (btw if you have a starting point to recommend)

I definitely do not like this fix, it destroys the elegance and the simplicity 
of the "single-dispatch" solution. And it introduce a lot of noisy code for a 
very rare case, people subclassing datetime.* classes.

Maybe making the regex dictionary having string keys instead of class and 
passing the correct string from the calling function, like:

def fromisoformat(string):
_parse_isodatetime('time', string)

or maybe functools.singledispatch handle this case ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[SilentGhost]

SilentGhost added the comment:

Mathieu, nothing was attached. The penalty's worth only a few if statements, I 
wouldn't worry too much about it. Besides, a C version is going to be provided 
as well, right?

Perhaps the following approach might solve the subclasses problem:

regex = dispatch.get(cls)
if not regex:
classes = datetime, date, time
cls = next((c for c in classes if issubclass(cls, c)), None)
if cls is None:   
raise TypeError
regex = dispatch[cls]

Perhaps, TypeError is unnecessary there and just propagating StopIteration 
would do. In that case the if clause would look like:

classes = datetime, date, time
cls = next(c for c in classes if issubclass(cls, c))
regex = dispatch[cls]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Aymeric Augustin]

Aymeric Augustin added the comment:

martin.panter: of course, I'm fine with integrating that code into Python.

deronnax: could you create a ticket on https://code.djangoproject.com/ 
highlighting the differences between Django's original implementation and the 
improved version that you worked on?

I'd like to use the stdlib implementation when it's available and align 
Django's current implementation to whatever's getting into the stdlib (to 
prepare the transition, even though we aren't going to drop support for Python 
3.5 soon).

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

SilentGhost: the dictionary single dispatch thing attached (apply on top of the 
last, fromisoformat_new3).
I mind the performance penalty for date-only parsing users, but the code is 
definitively shorter and more elegant.

But we have a major problem: tests fails because what is used in tests is a 
subclass of datetime classes (Subclass[Date|Time|DateTime]) and thus, the 
dispatch break with a KeyError: class.SubDate[...]. I have no idea on how 
mitigate that. Do you ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

New patch with all your concerns addressed (martin.panther+ silentghost) EXCEPT 
the single dispatch dictionary thing.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[SilentGhost]

Changes by SilentGhost :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

Hi Aymeric Augustin. I am guessing you are the original author of the code and 
tests in Django for parsing datetime strings 
(https://bugs.python.org/issue15873#msg260342). If so, would you be happy for 
it to be incorporated into Python?

Mathieu: I left a couple quick review comments. (Normally I leave a message in 
the main bug thread, but I forgot the other time.)

Doc strings: Generally I think we keep the doc strings to a minimum, and leave 
the main documentation for the RST files. For the RST documentation, I would 
suggest including a rough summary of the format. E.g. for time.fromisoformat(), 
something like “The string should be in the RFC’s ‘full-time’ format, which 
looks like HH:MM:SS[.mm][Z|±HH:MM].”

Now that you added the two new regex strings, I can see that it might be useful 
to keep them together, rather than next to each class. Or you could even make 
them class attributes. No strong opinions either way; whatever works for you I 
think.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

Crap, I just checked spams today and almost all mails of the reviewboard landed 
in spams ! So I made a new patch addressing all concerns:

* regex moved closer to where they're used
* regex globals start with an _
* case insensitive regex + handling(already handled in the previous revision)
* correct rounding + case suggested by Martin added as a test case
* more precise docstrings specifying that only a subset of ISO 8601 is accepted

bonus:
* useless non-capturing groups removed in regex, thus shorter and simpler

I still have a doubt though about the place I moved the regex. Tell me.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

OK, I know I post a lot, but this one should be the good one:
* recoded from scratch. Apart the algorithm, nothing come from Django anymore.
* help me fill the docstring, I'm not inspired
* datetime has few tests since it use the implementation of time._parse_time, 
which is heavily tested in time unittests.
* I now handle lowercase T and Z. (I know I could do "if tzinfo[0] in ('Z', 
'z')", but to me it feel like imposing a micro performance penalty to 
implementation correctly sending an uppercase Z)

I'm impatient to receive your feedback.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

(OK, I said a stupidity:  datetime's strptime handle microseconds. But time's 
one doesn't)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

simpler version using a simpler, stricter regex

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

Oh my god you're right. Thanks there is the re.ASCII flag.

2016-02-16 15:07 GMT+10:30 Martin Panter :

>
> Martin Panter added the comment:
>
> The regular expression r"\d" matches any digit in Unicode I think, not
> just ASCII digits 0-9. Perhaps we should limit it to ASCII digits. Or is it
> intended to allow non-ASCII digits like in "२०१६-०२-१६ ०१:२१:१४"?
>
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

The regular expression r"\d" matches any digit in Unicode I think, not just 
ASCII digits 0-9. Perhaps we should limit it to ASCII digits. Or is it intended 
to allow non-ASCII digits like in "२०१६-०२-१६ ०१:२१:१४"?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

The real question is : should we accept whatever iso8601 format is common to be 
found on the internet, or just be able to consume back the string issued by 
isoformat. From that results the answers to the questions you're asking: don't 
accept single digits, neither second-less datetime, ...
I don't really mind what the answer is. I'm OK for a stricter acceptance. I 
would like to ask ourselves : does a simpler, stricter implementation fulfill 
people needs ? If it's OK for you, it's OK for me.

By taking the Django version, I deviated the bit from the author's original 
need which was just being able to parse back datetime isoformat. The 
limitations he raises for not using strptime are gone now (strptime understand 
timezone), but it still can't understand microseconds nor optional parts (T or 
space for separator, optional microseconds). Even for a much simpler, stricter 
implementation, I'd like to stick with regex.

I'll do a date & time version, I just wait that we fall agree on the whole 
datetime thing.

Wether we change to a simpler code or keep it this way, I can rewrite tests & 
docstring.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

Martin Panter added the comment:

It looks to me like you copied a lot of code, doc strings, tests, etc from 

 and . I wouldn’t call it 
trivial. There is a BSD license for Django. Or do we have to get the relevant 
authors to do the Python CLA thing?

The current patch seems to allow a timezone without a colon, or even without 
minutes (+1100 and +11 as well as the RFC’s +11:00). Is this needed? The colon 
was made optional in Django in ; 
the argument given for this just seems to be ISO 8601 alignment, nothing 
practical. According to  Postgre 
SQL outputs time zones without the minutes field, but I don’t know if Python 
should go out of its way to support this obscure format.

RFC 3339 does not specify single digits in many places (e.g. 2016-2-1 1:0:0 is 
not specified). Should we also be stricter, at least for the minutes and 
seconds fields?

Also, is it necessary to allow the seconds field to be omitted, as in 
"2016-02-01 01:21"?

It seems that the “datetime” module does not support leap seconds, so if we 
mention RFC 3339 we should point out this inconsistency.

Victor: From my limited experiments, datetime.fromtimestamp() seems to use the 
round-to-even rule (not always rounding half up). Can you confirm? Maybe we 
should use that for consistency if it is practical. Otherwise, truncation 
towards zero would be the simplest.

As well as adding datetime.fromisoformat(), I think we should add similar 
methods to the separate date and time classes. One can parse the RFC’s 
full-date format fairly easily with strptime(), but not so for partial-time 
because of the fractional seconds.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

> I suggest to parse directly the string with C code, since the format looks 
> quite simple (numbers and a few separators).

But some of them are optional. And I would really like to mimic the same 
implementation logic in C.

Now I think the python version is fairly ready. What next ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

> No regex available at all in CPython?

It's not really convenient to use the re module in C.

> Otherwise, yeah, if I have to, I can do it with strptime.

I suggest to parse directly the string with C code, since the format looks 
quite simple (numbers and a few separators).

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

> Hum, you should use the same rounding method than
datetime.datetime.fromtimestamp(): ROUND_HALF_UP, as round().
In practice, you can for example pass a floating point number as
microseconds to datetime.datetime constructor.

Unfortunately, you're mistaking with the timedelta constructor. Datetime's one 
only take int :(
But I figured out an elegant manner to cope with (in my opinion)

> Since datetime is implemented in C, I'm not sure that using the re is
the best choice. Since the regex looks simple enough, we may parse the
string without the re module. Well, maybe only for the C
implementation.

No regex available at all in CPython ? Otherwise, yeah, if I have to, I can do 
it with strptime.

> What is the behaviour is there are spaces before/after the string?
What if there are other characters like letters before/after? You
should add an unit test for that. I expect an error when parsing
"t=2012-04-23T09:15:00" for example.
Your regex ends with $ but doesn't start with ^. Using re.match(), ^
and $ are probably not needed, but I'm not confident when I use regex
:-)

re.match only look at the beginning of the string, so no need for '^'. And 
therefore, the case
you mention is already handled :)

joined to this mail the last revision of the feature, with correct rounding, 
more test and one useless
line removed. Maybe the good one :) ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

> How does it parse this date:
> 2016-02-15T11:59:46.16588638674+09:00

Mathieu Dupuy added the comment:
> discarding the microseconds digits after the 6th.

Hum, you should use the same rounding method than
datetime.datetime.fromtimestamp(): ROUND_HALF_UP, as round().

In practice, you can for example pass a floating point number as
microseconds to datetime.datetime constructor.

Since datetime is implemented in C, I'm not sure that using the re is
the best choice. Since the regex looks simple enough, we may parse the
string without the re module. Well, maybe only for the C
implementation.

What is the behaviour is there are spaces before/after the string?
What if there are other characters like letters before/after? You
should add an unit test for that. I expect an error when parsing
"t=2012-04-23T09:15:00" for example.

Your regex ends with $ but doesn't start with ^. Using re.match(), ^
and $ are probably not needed, but I'm not confident when I use regex
:-)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

slightly improved + addresses issues stated here : 
https://bugs.python.org/review/15873/diff/16581/Lib/datetime.py#newcode1418Lib/datetime.py:1418

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

discarding the microseconds digits after the 6th.

2016-02-15 13:30 GMT+10:30 karl :

>
> karl added the comment:
>
> About
>
> > Actually, I realized that the best implementation of parsing rfc 3339
> > is in django dateparse utils. To me it's the finest, the most
> > elegant, and no other one can claim to be more robust since it's
> > probably the #1 iso parsing functions used in python. Have a look at
> >
> https://docs.djangoproject.com/en/1.9/_modules/django/utils/dateparse/#parse_datetime
>
> How does it parse this date:
>
> 2016-02-15T11:59:46.16588638674+09:00
>
> --
>
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> Python tracker 
> 
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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

About

> Actually, I realized that the best implementation of parsing rfc 3339 
> is in django dateparse utils. To me it's the finest, the most 
> elegant, and no other one can claim to be more robust since it's 
> probably the #1 iso parsing functions used in python. Have a look at 
> https://docs.djangoproject.com/en/1.9/_modules/django/utils/dateparse/#parse_datetime

How does it parse this date: 

2016-02-15T11:59:46.16588638674+09:00

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

>From https://www.djangoproject.com/foundation/cla/faq/

> Am I giving away the copyright to my contributions?
> 
> No. This is a pure license agreement, not a copyright assignment. You 
> still maintain the full copyright for your contributions. You are 
> only providing a license to the DSF to distribute your code without 
> further restrictions. This is not the case for all CLA's, but it is 
> the case for the one we are using.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

I don't know. The taken code is really little, modified, and is nothing much 
that an implementation you had seen a while ago, and recoded by memory not 
remembering where you saw it in the first place. Do you think that's really an 
issue ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

Is the django license compatible with the Python license?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

(slightly improved version, better use of timedelta)

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

Here is the PoC with code taken from django.utils.parse_datetime and adapted 
for the datetime module (I didn't ask for their agreement yet). Of course tests 
pass. For me it's the most elegant solution.

(I think date and time also need their "fromisotimestamp" counterpart).

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

#12006 will unfortunately of no use for this one.

Actually, I realized that the best implementation of parsing rfc 3339 is in 
django dateparse utils. To me it's the finest, the most elegant, and no other 
one can claim to be more robust since it's probably the #1 iso parsing 
functions used in python. Have a look at 
https://docs.djangoproject.com/en/1.9/_modules/django/utils/dateparse/#parse_datetime

Alexander, I won't start before I have your opinion. What do you think ?

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Jakub Stasiak]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

I'm working on the OpenStack project and iso8601 is heavily used.


> Otherwise, py8601 (https://bitbucket.org/micktwomey/pyiso8601/) looks pretty 
> popular and well maintained (various committers, started in 2012, last commit 
> in 2016).

I don't think that we should add the iso8601 module to the stdlib, but merge 
iso8601 "features" into the datetime module.

The iso8601 module supports Python 2.7 and so has to implement its own timezone 
classes. The datetime module now has datetime.timezone since Python 3.2 for 
fixed timezone.

The iso8601 module provides functions. I would prefer datetime.datetime 
*methods*.

Would you mind to try to implement that? It would be kind to contact iso8601 
author before.

The important part is also unit tests.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mathieu Dupuy]

Mathieu Dupuy added the comment:

So, shall we include it ? Otherwise, py8601 
(https://bitbucket.org/micktwomey/pyiso8601/) looks pretty popular and well 
maintained (various committers, started in 2012, last commit in 2016).
I think we should hurry, that's a great shame it has been while Python is able 
to generate a 8601 datetime but not parsing it back.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[STINNER Victor]

STINNER Victor added the comment:

See also #12006 for ISO 8601: "The datetime.strftime() and date.strftime() 
methods now support ISO 8601 date directives %G, %u and %V. (Contributed by 
Ashley Anderson in issue 12006.)".

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Mihai Capotă]

Changes by Mihai Capotă :


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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Piotr Dobrogost]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Jakub Wilk]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


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versions: +Python 3.6 -Python 3.4

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Ethan Furman]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Paul Bryan]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

After inspections, the best library for parsing RFC3339 style date is 
definitely:
https://github.com/tonyg/python-rfc3339/

Main code at
https://github.com/tonyg/python-rfc3339/blob/master/rfc3339.py

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

I had the issue today. I needed to parse a date with the following format.

2014-04-04T23:59:00+09:00

and could not with strptime.

I see a discussion in March 2014 
http://code.activestate.com/lists/python-ideas/26883/ but no followup. 

For references:
http://www.w3.org/TR/NOTE-datetime
http://tools.ietf.org/html/rfc3339

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

On closer inspection, Anders Hovmöller proposal doesn't work.
https://github.com/boxed/iso8601

At least for the microseconds part. 

In http://tools.ietf.org/html/rfc3339#section-5.6, the microsecond part is 
defined as:

time-secfrac= . 1*DIGIT

In http://www.w3.org/TR/NOTE-datetime, same thing:
 s= one or more digits representing a decimal fraction of a second

Anders considers it to be only six digits. It can be more or it can be less. :) 

Will comment on github too.

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[karl]

karl added the comment:

Noticed some people doing the same thing

https://github.com/tonyg/python-rfc3339
http://home.blarg.net/~steveha/pyfeed.html
https://wiki.python.org/moin/WorkingWithTime

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Iakov Davydov]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Ethan Furman]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Martin Panter]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Berker Peksag]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[R. David Murray]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Barry A. Warsaw]

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[issue15873] datetime: add ability to parse RFC 3339 dates and times

[Éric Araujo]

Éric Araujo added the comment:

John listed four modules with issues in the first message, and now we have 
proposals for two more modules.  Could you work together to make a unified 
patch?

Alexander, do you think there is a need to check python-ideas or python-dev 
before working on this?

(I changed the title to clarify scope: ISO 8601 is huge and not easily 
accessible whereas W3CDTF/RFC 3339 is narrower in scope and freely accessible.)

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title: datetime cannot parse ISO 8601 dates and times - datetime: add 
ability to parse RFC 3339 dates and times

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