classification
Title: Add ability to get tzinfo from a datetime instance in C API
Type: enhancement Stage: needs patch
Components: C API, Library (Lib) Versions: Python 3.9
process
Status: open Resolution:
Dependencies: 10381 Superseder:
Assigned To: Nosy List: atuining, belopolsky, dlenski, p-ganssle
Priority: normal Keywords:

Created on 2017-04-24 15:27 by atuining, last changed 2020-02-10 22:31 by p-ganssle.

Messages (4)
msg292230 - (view) Author: Anthony Tuininga (atuining) * Date: 2017-04-24 15:27
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!
msg321112 - (view) Author: Paul Ganssle (p-ganssle) * (Python committer) Date: 2018-07-05 15:54
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.
msg361722 - (view) Author: Anthony Tuininga (atuining) * Date: 2020-02-10 21:22
Any progress on this?
msg361737 - (view) Author: Paul Ganssle (p-ganssle) * (Python committer) Date: 2020-02-10 22:31
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 #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 (https://github.com/python/cpython/blob/d68e0a8a165761604e820c8cb4f20abc735e717f/Lib/test/datetimetester.py#L5914) 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)
History
Date User Action Args
2020-02-10 22:31:28p-gansslesettitle: Add ability to get/set tzinfo on datetime instances in C API -> Add ability to get tzinfo from a datetime instance in C API
stage: needs patch
messages: + msg361737
versions: + Python 3.9, - Python 3.6
2020-02-10 21:22:03atuiningsetmessages: + msg361722
2019-12-09 16:15:45belopolskysetdependencies: + Add timezone support to datetime C API
2019-12-09 16:13:43vstinnersetcomponents: + C API
2018-07-05 15:54:14p-gansslesetnosy: + p-ganssle
messages: + msg321112
2017-04-29 15:56:14xiang.zhangsetnosy: + belopolsky
2017-04-24 16:35:31dlenskisetnosy: + dlenski
2017-04-24 15:27:26atuiningcreate