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
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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}().