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Remove PyOS_ReadlineFunctionPointer from the stable ABI list #88034

encukou opened this issue Apr 16, 2021 · 3 comments

Remove PyOS_ReadlineFunctionPointer from the stable ABI list #88034

encukou opened this issue Apr 16, 2021 · 3 comments


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encukou commented Apr 16, 2021

BPO 43868
Nosy @pfmoore, @vstinner, @tjguk, @encukou, @zware, @zooba
  • bpo-43868: Remove PyOS_ReadlineFunctionPointer from the stable ABI list #25442
  • 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 2021-04-27.14:17:45.393>
    created_at = <Date 2021-04-16.14:48:28.426>
    labels = ['expert-C-API', '3.10', 'OS-windows']
    title = 'Remove PyOS_ReadlineFunctionPointer from the stable ABI list'
    updated_at = <Date 2021-04-27.14:17:45.393>
    user = '' fields:

    activity = <Date 2021-04-27.14:17:45.393>
    actor = 'vstinner'
    assignee = 'none'
    closed = True
    closed_date = <Date 2021-04-27.14:17:45.393>
    closer = 'vstinner'
    components = ['Windows', 'C API']
    creation = <Date 2021-04-16.14:48:28.426>
    creator = 'petr.viktorin'
    dependencies = []
    files = []
    hgrepos = []
    issue_num = 43868
    keywords = ['patch']
    message_count = 3.0
    messages = ['391206', '391237', '391690']
    nosy_count = 6.0
    nosy_names = ['paul.moore', 'vstinner', 'tim.golden', 'petr.viktorin', 'zach.ware', 'steve.dower']
    pr_nums = ['25442']
    priority = 'normal'
    resolution = 'fixed'
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = None
    url = ''
    versions = ['Python 3.10']

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    encukou commented Apr 16, 2021

    The inclusion of PyOS_ReadlineFunctionPointer in python3dll.c (*) was a mistake. According to PEP-384:

    functions expecting FILE* are not part of the ABI, to avoid depending on a specific version of the Microsoft C runtime DLL on Windows.

    The situation may have changed and it might be reasonable to revisit this decision, but that would call for a larger discussion. There are FILE*-taking functions that are probably much ore useful than this one. (But, I think it's a good idea to limit the stable ABI to file-like Python objects anyway.)

    I see PEP-384 as being definitive (where it's not ambiguous). The python3dll.c list and public/private headers do not actually define the stable ABI.

    So, I'd like to remove the function from the list.


    (*) it was actually PC/python3.def in 3.2

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    Yes, please remove it from the limited C API.

    PyOS_ReadlineFunctionPointer has a bad API. I fixed recently PyOS_StdioReadline because it used the Python C API without holding the GIL. To acquire the GIL, you need to access a *private* _PyOS_ReadlineTState variable which is kind of unfortunate :-(

    commit c353764
    Author: Victor Stinner <>
    Date: Mon Jun 1 20:59:35 2020 +0200

    bpo-40826: Fix GIL usage in PyOS_Readline() (GH-20579)
    Fix GIL usage in PyOS_Readline(): lock the GIL to set an exception.
    Pass tstate to my_fgets() and _PyOS_WindowsConsoleReadline(). Cleanup
    these functions.

    See also:

    commit fa7ab6a
    Author: Victor Stinner <>
    Date: Wed Jun 3 14:39:59 2020 +0200

    bpo-40826: Add _PyOS_InterruptOccurred(tstate) function (GH-20599)
    my_fgets() now calls _PyOS_InterruptOccurred(tstate) to check for
    pending signals, rather calling PyOS_InterruptOccurred().
    my_fgets() is called with the GIL released, whereas
    PyOS_InterruptOccurred() must be called with the GIL held.
    test_repl: use text=True and avoid SuppressCrashReport in
    Fix my_fgets() on Windows: fgets(fp) does crash if fileno(fp) is closed.

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    encukou commented Apr 23, 2021

    New changeset 91b69b7 by Petr Viktorin in branch 'master':
    bpo-43868: Remove PyOS_ReadlineFunctionPointer from the stable ABI list (GH-25442)

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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