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Expose PyErr_ChainExceptions in the stable API #89101

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Expose PyErr_ChainExceptions in the stable API#89101
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topic-C-APItype-featureA feature request or enhancement

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@pablogsal
pablogsal
opened on Aug 17, 2021
BPO 44938
Nosy @gpshead, @cjerdonek, @serhiy-storchaka, @pablogsal
PRs
  • bpo-44938: Expose PyErr_ChainExceptions in the stable API #27799
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    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 2021-08-17.17:44:23.749>
labels = ['expert-C-API', 'type-feature', '3.11']
title = 'Expose PyErr_ChainExceptions in the stable API'
updated_at = <Date 2021-12-10.19:07:14.668>
user = 'https://github.com/pablogsal'

    bugs.python.org fields:

    activity = <Date 2021-12-10.19:07:14.668>
actor = 'gregory.p.smith'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-08-17.17:44:23.749>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 44938
keywords = ['patch']
message_count = 6.0
messages = ['399777', '399820', '399835', '400101', '400107', '408245']
nosy_count = 4.0
nosy_names = ['gregory.p.smith', 'chris.jerdonek', 'serhiy.storchaka', 'pablogsal']
pr_nums = ['27799']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44938'
versions = ['Python 3.11']

    Activity

    1. pablogsal commented on Aug 17, 2021

      @pablogsal
      pablogsal
      on Aug 17, 2021
      MemberAuthor

      Currently, exception chaining in the C-API must be done by hand. This is a painstaking process that involves several steps and is very easy to do incorrectly.

      We currently have a private function: _PyErr_ChainExceptions that does this job. Given that exception chaining is a very fundamental operation, this functionality must be exposed in the stable C-API

    2. serhiy-storchaka commented on Aug 18, 2021

      @serhiy-storchaka
      serhiy-storchaka
      on Aug 18, 2021
      Member

      As the original author of _PyErr_ChainExceptions() (bpo-21715) I am not sure that its name and signature are optimal. It did not matter while it was internal function because we could change them at any moment, but for public API the design should be more thoughtful.

      Is passing three arguments convenient enough? Would not be better to pass them as a single argument like in _PyErr_ChainStackItem()? Is the function name good? Should we provide several similar functions for setting __context__, __cause__ and both?

      There are other, more specialized, helpers: _PyErr_FormatFromCause() and _PyErr_TrySetFromCause().

      There are also some flaws in setting __context__ and __cause__ (see bpo-39725). Perhaps we will design better concept of chaining exceptions in future.

    3. serhiy-storchaka
      added
      topic-C-API
      3.11only security fixes
      type-featureA feature request or enhancement
      on Aug 18, 2021

    4. pablogsal commented on Aug 18, 2021

      @pablogsal
      pablogsal
      on Aug 18, 2021
      MemberAuthor

      Serhiy, what do you suggest we should do then?

    5. cjerdonek commented on Aug 22, 2021

      @cjerdonek
      cjerdonek
      on Aug 22, 2021
      Member

      I agree with Serhiy that this API isn't necessarily the right one. It's just what happens to be there now. Also, we're still not clear on our stance towards cycles (see the bpo-25782 discussion). (Maybe the exposed version should result in an error if it would cause a cycle to be created.) Someone would need to think through what the API should be, though.

    6. pablogsal commented on Aug 22, 2021

      @pablogsal
      pablogsal
      on Aug 22, 2021
      MemberAuthor

      As long as the cycles don't actually end in a crash or an infinite cycle, I think is fine to not include them in the contact.

      Even if that were included I don't think is actually a problem. Many APIs in C or C++ require the user to not form cycles, for instance, shared pointers in the c++ stdlib.

    7. gpshead commented on Dec 10, 2021

      @gpshead
      gpshead
      on Dec 10, 2021
      Member

      related: https://www.python.org/dev/peps/pep-0490/ (rejected pep to auto-chain from C API calls)

      I don't come across it often, but I did just review some code at work today where the chain might have been nice (though not a big deal).

    8. ezio-melotti
      transferred this issue fromon Apr 10, 2022
    9. iritkatriel
      removed
      3.11only security fixes
      on May 10, 2023
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