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Some C buffer protocol APIs not documented #77307

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pitrou opened this issue Mar 23, 2018 · 9 comments
Closed

Some C buffer protocol APIs not documented #77307

pitrou opened this issue Mar 23, 2018 · 9 comments
Labels
3.7 (EOL) end of life 3.8 only security fixes docs Documentation in the Doc dir type-bug An unexpected behavior, bug, or error

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@pitrou
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pitrou commented Mar 23, 2018

BPO 33126
Nosy @pitrou, @skrah
PRs
  • bpo-33126: Document PyBuffer_ToContiguous() #6292
  • [3.6] bpo-33126: Document PyBuffer_ToContiguous() (GH-6292) #6293
  • [3.7] bpo-33126: Document PyBuffer_ToContiguous() (GH-6292) #6294
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    Files
  • issue33126.diff
    		•

    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 2018-03-28.15:50:58.906>
created_at = <Date 2018-03-23.16:49:06.181>
labels = ['3.8', 'type-bug', '3.7', 'docs']
title = 'Some C buffer protocol APIs not documented'
updated_at = <Date 2018-03-28.15:50:58.905>
user = 'https://github.com/pitrou'

    bugs.python.org fields:

    activity = <Date 2018-03-28.15:50:58.905>
actor = 'pitrou'
assignee = 'docs@python'
closed = True
closed_date = <Date 2018-03-28.15:50:58.906>
closer = 'pitrou'
components = ['Documentation']
creation = <Date 2018-03-23.16:49:06.181>
creator = 'pitrou'
dependencies = []
files = ['47497']
hgrepos = []
issue_num = 33126
keywords = ['patch']
message_count = 9.0
messages = ['314315', '314387', '314388', '314424', '314425', '314605', '314608', '314611', '314612']
nosy_count = 3.0
nosy_names = ['pitrou', 'skrah', 'docs@python']
pr_nums = ['6292', '6293', '6294']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33126'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']
    @pitrou
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    pitrou commented Mar 23, 2018

    The following C functions are available for C code but not documented:

    • PyBuffer_ToContiguous()
    • PyBuffer_FromContiguous()
    • PyObject_CopyData()

    I am not sure how to describe those functions myself.

    @pitrou pitrou added 3.7 (EOL) end of life 3.8 only security fixes labels Mar 23, 2018
    @pitrou pitrou added docs Documentation in the Doc dir type-bug An unexpected behavior, bug, or error labels Mar 23, 2018
    @skrah
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    skrah mannequin commented Mar 24, 2018

    I fixed PyBuffer_ToContiguous() in 3.3, PyBuffer_FromContiguous() was broken until bpo-23370.

    For a start, here's a doc patch for PyBuffer_ToContiguous().

    PyBuffer_FromContiguous() does the opposite and loads a contiguous buffer
    into a possibly non-contiguous view.

    PyObject_CopyData() copies the data from exporter src to the writable exporter dest.

    I have never used the last two functions.

    @pitrou
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    pitrou commented Mar 24, 2018

    Thanks. The PyBuffer_ToContiguous() API is weird: why pass len if it cannot be anything other than src->len?
    Also, it would be nice to explain whether the actual buffer data is copied around (with a memory allocation?) or if it's just the Py_buffer struct.

    @skrah
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    skrah mannequin commented Mar 25, 2018

    Yes, the signatures are weird. In PyBuffer_FromContiguous(), "len" is
    the size of "buf" in bytes.

    If "buf" contains 6 floats, but "view" only has space for 4, then only
    4 are copied into "view".

    To avoid that sort of thing, I changed PyBuffer_ToContiguous() to
    be more restrictive in 3.3, but kept the len parameter.

    In PyBuffer_ToContiguous() it would not matter though if len(buf) > src->len, in which case buf would contain uninitialized bytes at
    the end.

    TBH, I don't think these functions are used very often. :-)

    @skrah
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    Mannequin

    skrah mannequin commented Mar 25, 2018

    And if view->len > len in PyBuffer_FromContiguous(), then
    view will contain uninitialized bytes, which is bad.

    @pitrou
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    pitrou commented Mar 28, 2018

    Ok, it seems only PyBuffer_ToContiguous() is worth documenting.

    @pitrou
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    pitrou commented Mar 28, 2018

    New changeset aa50bf0 by Antoine Pitrou in branch 'master':
    bpo-33126: Document PyBuffer_ToContiguous() (bpo-6292)
    aa50bf0

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    pitrou commented Mar 28, 2018

    New changeset 18fdc87 by Antoine Pitrou (Miss Islington (bot)) in branch '3.6':
    bpo-33126: Document PyBuffer_ToContiguous() (GH-6292) (GH-6293)
    18fdc87

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    pitrou commented Mar 28, 2018

    New changeset 6124d8e by Antoine Pitrou (Miss Islington (bot)) in branch '3.7':
    bpo-33126: Document PyBuffer_ToContiguous() (GH-6292) (GH-6294)
    6124d8e

    @pitrou pitrou closed this as completed Mar 28, 2018
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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