Add ability to get tzinfo from a datetime instance in C API

[atuining]

BPO	30155
Nosy	@abalkin, @pitrou, @dlenski, @pganssle, @ZackerySpytz
PRs	bpo-30155: Add macros to get tzinfo from datetime instances #21633
Dependencies	bpo-10381: Add timezone support to datetime C API

^{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 = <Date 2020-10-21.19:51:20.376>
created_at = <Date 2017-04-24.15:27:26.203>
labels = ['expert-C-API', 'type-feature', 'library', '3.10']
title = 'Add ability to get tzinfo from a datetime instance in C API'
updated_at = <Date 2020-10-21.19:51:20.376>
user = 'https://bugs.python.org/atuining'

bugs.python.org fields:

activity = <Date 2020-10-21.19:51:20.376>
actor = 'p-ganssle'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-21.19:51:20.376>
closer = 'p-ganssle'
components = ['Library (Lib)', 'C API']
creation = <Date 2017-04-24.15:27:26.203>
creator = 'atuining'
dependencies = ['10381']
files = []
hgrepos = []
issue_num = 30155
keywords = ['patch']
message_count = 7.0
messages = ['292230', '321112', '361722', '361737', '374009', '374354', '377417']
nosy_count = 6.0
nosy_names = ['atuining', 'belopolsky', 'pitrou', 'dlenski', 'p-ganssle', 'ZackerySpytz']
pr_nums = ['21633']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue30155'
versions = ['Python 3.10']

[atuining]

Right now there is no documented way to create a datetime instance with a tzinfo instance. The documented macros all hard code the value Py_None for the tzinfo parameter. Using the PyObject_Call() method instead of the macro for creating a datetime instance is ~5x slower.

In addition, there is no macro or method for getting the tzinfo from an existing datetime instance. Perhaps creating DATE_GET_TZINFO and TIME_GET_TZINFO would be acceptable?

The enhancement 10381 (http://bugs.python.org/issue10381) would also be needed.

I can provide a GitHub PR if that would be helpful. I first want to make sure that such an effort would be appreciated!

[pganssle]

Hmm. I never noticed this. In the past I have used the (undocumented) PyDateTimeAPI struct, which the official macros wrap. I'm not sure how official that struct is considering it doesn't show up in the documentation.

I agree that it should be possible to construct TZ-aware datetimes using the official C API, so I guess the question is whether to add a bunch more macros or document the existing struct.

[atuining]

Any progress on this?

[pganssle]

So this bug is asking for two things:

1. An official accessor for the tzinfo component of an existing datetime, which I think is very reasonable in light of the fact that there are official accessors for all the other components of a datetime.

2. An official constructor for a timezone-aware datetime, which I think basically exists in the form of PyDatetime_CAPI->PyDateTimeAPI->DateTime_FromDateAndTime / ->DateTime_FromDateAndTimeAndFold, and we just need to document it. I think this is basically a separate issue, and I have opened bpo-39604 to track it.

I'm going to rename this bug to focus only on issue #1. I think we can accept a PR adding two new macros. I would suggest calling them:

• PyDateTime_DATE_GET_TZINFO
• PyDateTime_TIME_GET_TZINFO

Please make sure to add tests to any PR you make. See the CapiTest case (

cpython/Lib/test/datetimetester.py

Line 5914 in d68e0a8

class CapiTest(unittest.TestCase):

) for examples. You may want to look at the git blame for a few of those tests to see the PRs that they were added in, since part of the tests are defined in a C file.

(As an aside: I don't love that the accessor methods are not available on the struct, since all the "macro-only" code needs to be re-implemented in all other-language bindings. Since the accessors are already all macro-only, though, might as well keep with the tradition for now :P)

[pitrou]

I'm going to rename this bug to focus only on issue #1. I think we can accept a PR adding two new macros. I would suggest calling them:

• PyDateTime_DATE_GET_TZINFO
• PyDateTime_TIME_GET_TZINFO

+1 for this.

[ZackerySpytz]

I have created PR 21633 to add these macros. Please consider taking a look.

[pganssle]

New changeset 2e4dd33 by Zackery Spytz in branch 'master':
bpo-30155: Add macros to get tzinfo from datetime instances (GH-21633)
2e4dd33