Add datetime.time.strptime and datetime.date.strptime

[josh-sf]

BPO	1100942
Nosy	@amauryfa, @abalkin, @vstinner, @devdanzin, @berkerpeksag, @soltysh, @matrixise, @vajrasky, @matheusportela, @pganssle
PRs	WIP: bpo-1100942: Add datetime.time.strptime and datetime.date.strptime #5578
Files	strptime.diff strptime2.diff: time.strptime and date.strptime as well date-strptime.patch issue1100942.diff issue1100942_pure.diff issue1100942_pure2.diff issue1100942_v4.diff issue1100942_full.patch: Full (merged) patch against current HEAD issue1100942_20140409.patch: Patch fixed against current default branch issue1100942.patch issue1100942-3.6.patch issue1100942_20170722.patch

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

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2005-01-12.14:53:01.000>
labels = ['extension-modules', 'type-feature', '3.8']
title = 'Add datetime.time.strptime and datetime.date.strptime'
updated_at = <Date 2018-08-20.19:46:06.268>
user = 'https://bugs.python.org/josh-sf'

bugs.python.org fields:

activity = <Date 2018-08-20.19:46:06.268>
actor = 'p-ganssle'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2005-01-12.14:53:01.000>
creator = 'josh-sf'
dependencies = []
files = ['6427', '6428', '14351', '17599', '26446', '26452', '29117', '33240', '34778', '39345', '44044', '47032']
hgrepos = []
issue_num = 1100942
keywords = ['patch', 'needs review']
message_count = 48.0
messages = ['47516', '47517', '47518', '47519', '47520', '82109', '89650', '103731', '103732', '106805', '106807', '107402', '114247', '126013', '162732', '165882', '165905', '165906', '165929', '174743', '174746', '182336', '184577', '206495', '206498', '206500', '206519', '206717', '215472', '215474', '215491', '215537', '215559', '215843', '242569', '242803', '242809', '242917', '272149', '273568', '279331', '279333', '279334', '298841', '298842', '311783', '313948', '321550']
nosy_count = 22.0
nosy_names = ['jafo', 'guettli', 'amaury.forgeotdarc', 'belopolsky', 'sonderblade', 'alanvgreen', 'vstinner', 'ajaksu2', 'josh-sf', 'cvrebert', 'tiktuk', 'adam-collard', 'westley.martinez', 'berker.peksag', 'maciej.szulik', 'Juarez.Bochi', 'petre', 'matrixise', 'vajrasky', 'Julian.Gindi', 'matheus.v.portela', 'p-ganssle']
pr_nums = ['5578']
priority = None
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue1100942'
versions = ['Python 3.8']

Linked PRs

• gh-41431: Add datetime.time.strptime() and datetime.date.strptime() #120752

[josh-sf]

Alllow creating new datetime objects by parsing date
strings.

datetime already has strftime, so adding strptime is
logical.

The new constructor is equivalent to
datetime(*(time.strptime(date_string, format)[0:6])).

Patch includes documentation and unit test.

[alanvgreen]

Logged In: YES
user_id=1174944

This patch will be welcomed by all of that have had to write
"datetime(*(time.strptime(date_string, format)[0:6]))".

I don't understand the C API well enough to check if
reference counts are handled properly, but otherwise the
implementation looks straight forward.

Documentation looks good and the test passes on my machine.

Two suggestions:

1. In the time module, the strptime() function's format
   parameter is optional. For consistency's sake, I'd expect
   datetime.strptime()'s format parameter also to be optional.
   (On the other hand, the default value for the format is not
   very useful.)

2. Since strftime is supported by datetime.time,
   datetime.date and datetime.datetime, I'd also expect
   strptime to be supported by all three classes. Could you add
   that now, or would it be better to do it as a separate patch?

[josh-sf]

Logged In: YES
user_id=1194964

Regarding support by datetime.time and datetime.date, if a
date component or a time component is specified,
respectively, do you think that we should raise an
exception? or should we just ignore it?

[josh-sf]

Logged In: YES
user_id=1194964

The first patch has been applied, now just the second needs
to be. (strptime2.diff).

That adds support for date and time as well as datetime, as
per alanvgreen's suggestion.

[sonderblade]

The patch doesn't apply cleanly anymore, although that was easy to fix. With the patch, I also get a few implicit declaration warnings and a few conflicting type errors. Rearranging the order of the functions solve that. Fixing that makes the code compile. The two new methods seem to work correct, although there should be unit tests.

[devdanzin]

Patch needs updating.

[amauryfa]

Here is an updated patch, with tests.

The only thing that bugs me is the name of the method: date.strptime()
seems a bit odd, given that it cannot accept a time part...
OTOH 'strptime' refers to the format specification: %Y-%m-%d

[AlexanderBelopolsky]

I am +1 for adding these features and I have only one comment on the code:

It is documented in time.strptime() documentation that
"""
The default values used to fill in any missing data when more accurate values cannot be inferred are (1900, 1, 1, 0, 0, 0, 0, 1, -1).
""" http://docs.python.org/dev/py3k/library/time.html#time.strptime

and "datetime.strptime(date_string, format) is equivalent to datetime(*(time.strptime(date_string, format)[0:6]))." according to datetime module documentation.

Thus, datetime.strptime("", "") returning datetime.datetime(1900, 1, 1, 0, 0) is not an implementation detail and there is no need to compute it in time_strptime.

[AlexanderBelopolsky]

BTW, it does not bother me that "date.strptime()
seems a bit odd, given that it cannot accept a time part." To me "time" in strptime means time specification that may include date, time or even just month. If parsed specification does not fit in date (includes time component), date.strptime fails. There is nothing wrong with it. An alternative would be to make {date,time}.strptime() promiscuous and just drop unneeded components, but that would make these functions less useful because such behavior is simply datetime.strptime(..).{date,time}().

[abalkin]

Does this need to be brought up on python-dev for acceptance?

[mdickinson]

This doesn't appear to be at all controversial; I don't think it's necessary to consult python-dev. (I haven't looked at the patch, though.)

[abalkin]

I have updated Amaury's patch for py3k. I simplified the test for default date values and fixed a documentation nit. (Time fileds are [4:7], not [4:6]). The result is attached as bpo-1100942.diff.

Note that date.strptime accepts some time specs and time.strptime accepts some date specs:

>>> time.strptime('1900', '%Y')
datetime.time(0, 0)
>>> date.strptime('00', '%H')
datetime.date(1900, 1, 1)

This matches the proposed documentation, but I am not sure is desirable.
I am about +0 for making the test more robust by scanning the format string and rejecting date format codes in time.strptime and time format codes in date. This will also allow better diagnostic messages. For example, instead of

>>> date.strptime('01', '%M')
Traceback (most recent call last):
  ..
ValueError: date.strptime value cannot have a time part

we can produce "'%M' is not valid in date format specification."

[abalkin]

Is anyone still interested in moving this forward?

[abalkin]

New patch needed to address the issue of time.strftime() accepting %Y when year is 1900 and other similar oddities. See msg107402 above. Also a patch for datetime.py is needed.

[abalkin]

Bumping priority to get this in before beta.

[JuarezBochi]

I have updated the patches since they were not applying cleanly and included a pure Python implementation that was missing.

It has the same issues that were mentioned on msg107402.

Do you have any suggestions? I'm planning to block the formats that are not allowed and raise Exceptions like suggested before:

>>> date.strptime('01', '%M')
...
"'%M' is not valid in date format specification."

[JuarezBochi]

I've updated my patch with the tests for datetime.time.strptime that were missing and also its pure Python implementation.

The previous diff also had some issues that I've fixed now: duplicated datetime.strptime method definition in c and the pure python docstring state that date.strpdate was a method and not a constructor.

[JuarezBochi]

Sorry. I updated my patch again to fix the exception message for time.strptime in the pure Python version.

[JuarezBochi]

I've updated the patch based on ezio.melotti and berkerpeksag reviews (thanks).

It's still missing the modifications proposed on msg107402.

[BreamoreBoy]

Could someone please review this with a view to getting the patch into the 3.4 code base, thanks.

[abalkin]

Juarez,

Are you planning to implement format validation as you described in msg165882? Without that, date.strptime() is not very useful because it is almost equivalent to datetime.strptime().date().

[berkerpeksag]

New patch attached.

Changes:

• Addressed msg107402. I will update the C code if this implementation
  is correct.
• Added more tests
• Converted classmethods to staticmethods
• Removed doctests
• Updated documentation

[jafo]

I've tried to test this but v4 doesn't apply cleanly after pure2 is applied, and v4 doesn't include enough to test it (applying v4 only causes test failures).

I reviewed v4 and it looks fine in general. I do see that there are changes in it unrelated to this issue, but they are PEP-8 changes so I'm not objecting, but ideally that would be split out into a separate patch.

I think that this code will incorrectly detect something like '%s %%wall clock' as a date spec because it contains '%w', but strptime would consider that '%' followed by the string 'wall'. A subtle edge case, but worth considering. Maybe it needs to strip out %% first then look for the % sequences? Or perhaps just do the conversion and if the Y/M/D fields are set in then decide that it included a date spec, or if the HMS are set then say that it has the time spec included?

[soltysh]

Berker per your comment updated patch changing those two new methods (namely date.strptime and time.strptime) to be classmethod and not staticmethods.

[matrixise]

Here is an updated version (for 3.6) of the patch of maciej.szulik.

I have executed all the tests.

Please, could you review this patch.

Thank you

[abalkin]

This does not look right:

+.. classmethod:: time.strptime(date_string, format)
+
+ Return a :class:`time` corresponding to *date_string, parsed according to
+ *format*. :exc:`ValueError` is raised if the date string and format can't be
+ parsed by `time.strptime`, if it returns a value which isn't a time tuple,
+ or if the time part is nonzero.
^^^^^^^^^

[matrixise]

belopolsky, could you tell me what it is wrong with the doc about time.strptime ?

[abalkin]

Shouldn't "time part" underlined in my previous note be "date part" instead? Also, does non-zero mean non-empty?

[abalkin]

Never mind the second question.

[matheusportela]

The patch is broken against Python 3.7. I'll try working on it.

[matheusportela]

Also, may I move this issue to a GitHub PR?

[matrixise]

I have updated the patch for 3.8, create a PR and fixed the documentation of _strptime._strptime, because this function returns a 3-tuple and not a 2-tuple as indicated in its comment.

Thank you

[matrixise]

Hello, just a small reminder for this issue and the PR ;-) when you have time

[vstinner]

I removed the easy keyword from this issue: it's open since 2005, it has 12 patches and 1 PR attached, and a lot of discussion.

[abalkin]

I have updated the patch for 3.8, create a PR ..

@matrixise, I don't see a PR linked to this issue.

[abalkin]

Found it: GH-5578.