Implement PyObject_CopyToObject

[nanjekyejoannah]

BPO	39835
Nosy	@nanjekyejoannah

^{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 2020-03-03.15:18:33.166>
labels = ['expert-C-API', 'type-feature', '3.9']
title = 'Implement PyObject_CopyToObject'
updated_at = <Date 2020-03-03.15:18:33.166>
user = 'https://github.com/nanjekyejoannah'

bugs.python.org fields:

activity = <Date 2020-03-03.15:18:33.166>
actor = 'nanjekyejoannah'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2020-03-03.15:18:33.166>
creator = 'nanjekyejoannah'
dependencies = []
files = []
hgrepos = []
issue_num = 39835
keywords = []
message_count = 1.0
messages = ['363264']
nosy_count = 1.0
nosy_names = ['nanjekyejoannah']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39835'
versions = ['Python 3.9']

Linked PRs

• gh-84016: Implement missing PyObject_CopyToObject in PEP3118 #124747

[nanjekyejoannah]

I suggest implementing a C-API for copying data into a buffer exported by an obj. i.e

int PyObject_CopyToObject(PyObject *obj, void *buf, Py_ssize_t len,
                          char fortran)

as was intended in PEP-3118. The documentation there says this functionality should:

"Copy len bytes of data pointed to by the contiguous chunk of memory pointed to by buf into the buffer exported by obj. Return 0 on success and return -1 and raise an error on failure. If the object does not have a writable buffer, then an error is raised. If fortran is 'F', then if the object is multi-dimensional, then the data will be copied into the array in Fortran-style (first dimension varies the fastest). If fortran is 'C', then the data will be copied into the array in C-style (last dimension varies the fastest). If fortran is 'A', then it does not matter and the copy will be made in whatever way is more efficient."

[JelleZijlstra]

PEP-3118 was written 18 years ago and we've managed without this function for that long. I think we should add it only if there are clear use cases, not simply because it's in the PEP.

If you'd like this function implemented, could you provide examples of existing code (e.g., in existing C extensions) that would be made better by this function?

[vstinner]

I just close the issue. If someone wants to reopen the issue, please come with convincing examples. Not just a reference to an old PEP.