[ExceptionGroup] Inconsistent raise inside except* #103590

andriilahuta · 2023-04-17T14:34:03Z

Bug report

When raising inside except* block and the caught exception wasn't an ExceptionGroup originally, then raised exception doesn't get wrapped in ExceptionGroup:

try:
    try:
        raise TypeError(1)  # prints ValueError(3)
        raise ExceptionGroup('', [TypeError(2)])  # prints ExceptionGroup('', [ValueError(3)])
    except* TypeError:
        raise ValueError(3)
except BaseException as e:
    print(repr(e))

Your environment

CPython versions tested on: 3.11.3
Operating system and architecture: Windows 11 / Ubuntu 22.04

Linked PRs

mdboom · 2023-04-17T16:04:47Z

Cc: @iritkatriel

sunmy2019 · 2023-04-17T16:30:57Z

This is fully documented behavior. https://peps.python.org/pep-0654/#raising-new-exceptions

Raising a new instance of a naked exception does not cause this exception to be wrapped by an exception group. Rather, the exception is raised as is, and if it needs to be combined with other propagated exceptions, it becomes a direct child of the new exception group created for that.

>>> try:
...     raise ExceptionGroup("eg", [ValueError('a')])
... except* ValueError:
...     raise KeyError('x')
...
  | ExceptionGroup:  (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "<stdin>", line 2, in <module>
    | ExceptionGroup: eg (1 sub-exception)
    +-+---------------- 1 ----------------
      | ValueError: a
      +------------------------------------
    |
    | During handling of the above exception, another exception occurred:
    |
    | Traceback (most recent call last):
    |   File "<stdin>", line 4, in <module>
    | KeyError: 'x'
    +------------------------------------
>>>
>>> try:
...     raise ExceptionGroup("eg", [ValueError('a'), TypeError('b')])
... except* ValueError:
...     raise KeyError('x')
...
  | ExceptionGroup:  (2 sub-exceptions)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "<stdin>", line 2, in <module>
    | ExceptionGroup: eg (1 sub-exception)
    +-+---------------- 1 ----------------
      | ValueError: a
      +------------------------------------
    |
    | During handling of the above exception, another exception occurred:
    |
    | Traceback (most recent call last):
    |   File "<stdin>", line 4, in <module>
    | KeyError: 'x'
    +---------------- 2 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "<stdin>", line 2, in <module>
    | ExceptionGroup: eg (1 sub-exception)
    +-+---------------- 1 ----------------
      | TypeError: b
      +------------------------------------
>>>

andriilahuta · 2023-04-17T18:03:44Z

@sunmy2019 thanks for the docs pointer. It is a bit confusing behavior for me, since I can't always be sure what I'm actually raising. But I guess we can close this then?

carljm · 2023-04-17T23:52:16Z

I don't think that the issue in the OP here clearly matches any example shown in the PEP. The key factor in the PEP example:

>>> try:
...     raise ExceptionGroup("eg", [ValueError('a'), TypeError('b')])
... except* ValueError:
...     raise KeyError('x')

is that the raised exception group includes both a ValueError (will be caught by the except* ValueError) and a TypeError (is not caught and thus must be propagated.) It is the latter TypeError that means the newly raised KeyError "needs to be combined with other propagated exceptions" (the TypeError), and thus a new ExceptionGroup is created for that.

In the OP example:

try:
    raise ExceptionGroup('', [TypeError(2)])
except* TypeError:
    raise ValueError(3)

the original exception group contains only a TypeError, which is caught by except* TypeError. So there are no remaining uncaught exceptions that must propagate along with the newly raised ValueError. So according to the wording in the PEP:

Rather, the exception is raised as is, and if it needs to be combined with other propagated exceptions, it becomes a direct child of the new exception group created for that

it is surprising (to me -- not an expert in the ExceptionGroup feature by any means) that a new ExceptionGroup would be created containing just the newly-raised ValueError.

The documentation says about this case:

Any remaining exceptions that were not handled by any except* clause are re-raised at the end, combined into an exception group along with all exceptions that were raised from within except* clauses.

This wording is more ambiguous than the wording in the PEP, and leaves open the possibility that a new exception group should always be created, even if we are raising just a single exception and there were no "remaining exceptions" to propagate.

So it is possible this is intended behavior, but it doesn't seem at all clear. I think we need input from @iritkatriel here.

…ept*

iritkatriel · 2023-04-21T16:15:19Z

I agree that the wording of the PEP implies that wrapping in an exception group should not happen unless it is necessary, and it is not necessary when there is only one exception.

I don't remember why I implemented it this way (with unit tests asserting this behaviour, no less). I'm going to assume that it was a simple mistake and make a PR to fix it. Will ask @gvanrossum for a second option.

…103665)

…ept* (python#103665)

…cept* (#104094)

…except* documentation (#104095)

793: Bump exceptiongroup from 1.1.1 to 1.1.2 r=alallema a=dependabot[bot] Bumps [exceptiongroup](https://github.com/agronholm/exceptiongroup) from 1.1.1 to 1.1.2. <details> <summary>Changelog</summary> Sourced from <a href="https://github.com/agronholm/exceptiongroup/blob/main/CHANGES.rst">exceptiongroup's changelog</a>. <blockquote> <h1>Version history</h1> This library adheres to <code>Semantic Versioning 2.0 <http://semver.org/></code>_. 1.1.2 <ul> <li>Changed handling of exceptions in exception group handler callbacks to not wrap a single exception in an exception group, as per <code>CPython issue 103590 <https://github.com/python/cpython/issues/103590></code>_</li> </ul> 1.1.1 <ul> <li>Worked around <code>CPython issue [#98778](https://github.com/agronholm/exceptiongroup/issues/98778) <https://github.com/python/cpython/issues/98778></code>_, <code>urllib.error.HTTPError(..., fp=None)</code> raises <code>KeyError</code> on unknown attribute access, on affected Python versions. (PR by Zac Hatfield-Dodds)</li> </ul> 1.1.0 <ul> <li>Backported upstream fix for <a href="https://redirect.github.com/agronholm/exceptiongroup/issues/99553">gh-99553</a> (custom subclasses of <code>BaseExceptionGroup</code> that also inherit from <code>Exception</code> should not be able to wrap base exceptions)</li> <li>Moved all initialization code to <code>__new__()</code> (thus matching Python 3.11 behavior)</li> </ul> 1.0.4 <ul> <li>Fixed regression introduced in v1.0.3 where the code computing the suggestions would assume that both the <code>obj</code> attribute of <code>AttributeError</code> is always available, even though this is only true from Python 3.10 onwards (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/43">#43</a>; PR by Carl Friedrich Bolz-Tereick)</li> </ul> 1.0.3 <ul> <li>Fixed monkey patching breaking suggestions (on a <code>NameError</code> or <code>AttributeError</code>) on Python 3.10 (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/41">#41</a>; PR by Carl Friedrich Bolz-Tereick)</li> </ul> 1.0.2 <ul> <li>Updated type annotations to match the ones in <code>typeshed</code></li> </ul> 1.0.1 <ul> <li>Fixed formatted traceback missing exceptions beyond 2 nesting levels of <code>__context__</code> or <code>__cause__</code></li> </ul> 1.0.0 <ul> <li>Fixed <code>AttributeError: 'PatchedTracebackException' object has no attribute '__cause__'</code> on Python 3.10 (only) when a traceback is printed from an exception where an exception</li> </ul>  </blockquote> ... (truncated) </details> <details> <summary>Commits</summary> <ul> <li><a href="https://github.com/agronholm/exceptiongroup/commit/571b12187c0eee916ad224f670fb7739b94fddc7"><code>571b121</code></a> Added the release version</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/821d5ebaadfd0b5b16c785a942f69e89933217bf"><code>821d5eb</code></a> Changed handling of a single exception raised in exception group handlers to ...</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/8a104ebc3f0201b5af0787bc90d09522f43e1d4c"><code>8a104eb</code></a> Fixed pre-commit error</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/cad96f68f9ddbb8d347ebe9c26544e26f99584f7"><code>cad96f6</code></a> Added .ruff_cache/ to .gitignore</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/111f33842e2ed91ad795d29d6ca4a1d493f6684d"><code>111f338</code></a> Fixed coveralls reporting</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/c926b0a0c1d6a4755382fb0ff0cc929cc28904b8"><code>c926b0a</code></a> Switched from flake8 and isort to ruff</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/0d6338707a1ff6e0dfcf4ffc392609b1cd7c16cd"><code>0d63387</code></a> Added Python 3.12 to the testing matrix</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/9bfc03f402cca2d671a42d00dafb56f5c1e75847"><code>9bfc03f</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/63">#63</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/c604dd818b7dd3b8817594fce048a6f85870832a"><code>c604dd8</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/62">#62</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/516e53262eb4608266f6b314764d2be23900ce1c"><code>516e532</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/61">#61</a>)</li> <li>Additional commits viewable in <a href="https://github.com/agronholm/exceptiongroup/compare/1.1.1...1.1.2">compare view</a></li> </ul> </details> [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=exceptiongroup&package-manager=pip&previous-version=1.1.1&new-version=1.1.2)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) You can trigger a rebase of this PR by commenting ``@dependabot` rebase`. 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https://build.opensuse.org/request/show/1096944 by user mcepl + favogt_factory - Update to 1.1.2: - Changed handling of exceptions in exception group handler callbacks to not wrap a single exception in an exception group, as per CPython issue gh#python/cpython#103590. - Add skip-test_catch_handler_raises-for-older-311.patch (gh#agronholm/exceptiongroup#64).

837: Bump exceptiongroup from 1.1.2 to 1.1.3 r=sanders41 a=dependabot[bot] Bumps [exceptiongroup](https://github.com/agronholm/exceptiongroup) from 1.1.2 to 1.1.3. <details> <summary>Changelog</summary> Sourced from <a href="https://github.com/agronholm/exceptiongroup/blob/main/CHANGES.rst">exceptiongroup's changelog</a>. <blockquote> <h1>Version history</h1> This library adheres to <code>Semantic Versioning 2.0 <http://semver.org/></code>_. 1.1.3 <ul> <li><code>catch()</code> now raises a <code>TypeError</code> if passed an async exception handler instead of just giving a <code>RuntimeWarning</code> about the coroutine never being awaited. (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/66">#66</a>, PR by John Litborn)</li> <li>Fixed plain <code>raise</code> statement in an exception handler callback to work like a <code>raise</code> in an <code>except*</code> block</li> <li>Fixed new exception group not being chained to the original exception when raising an exception group from exceptions raised in handler callbacks</li> <li>Fixed type annotations of the <code>derive()</code>, <code>subgroup()</code> and <code>split()</code> methods to match the ones in typeshed</li> </ul> 1.1.2 <ul> <li>Changed handling of exceptions in exception group handler callbacks to not wrap a single exception in an exception group, as per <code>CPython issue 103590 <https://github.com/python/cpython/issues/103590></code>_</li> </ul> 1.1.1 <ul> <li>Worked around <code>CPython issue [#98778](https://github.com/agronholm/exceptiongroup/issues/98778) <https://github.com/python/cpython/issues/98778></code>_, <code>urllib.error.HTTPError(..., fp=None)</code> raises <code>KeyError</code> on unknown attribute access, on affected Python versions. (PR by Zac Hatfield-Dodds)</li> </ul> 1.1.0 <ul> <li>Backported upstream fix for <a href="https://redirect.github.com/agronholm/exceptiongroup/issues/99553">gh-99553</a> (custom subclasses of <code>BaseExceptionGroup</code> that also inherit from <code>Exception</code> should not be able to wrap base exceptions)</li> <li>Moved all initialization code to <code>__new__()</code> (thus matching Python 3.11 behavior)</li> </ul> 1.0.4 <ul> <li>Fixed regression introduced in v1.0.3 where the code computing the suggestions would assume that both the <code>obj</code> attribute of <code>AttributeError</code> is always available, even though this is only true from Python 3.10 onwards (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/43">#43</a>; PR by Carl Friedrich Bolz-Tereick)</li> </ul> 1.0.3 <ul> <li>Fixed monkey patching breaking suggestions (on a <code>NameError</code> or <code>AttributeError</code>) on Python 3.10 (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/41">#41</a>; PR by Carl Friedrich Bolz-Tereick)</li> </ul> 1.0.2  </blockquote> ... (truncated) </details> <details> <summary>Commits</summary> <ul> <li><a href="https://github.com/agronholm/exceptiongroup/commit/31d77ffefa298eb6ab73a97c8cde0c3d5a535983"><code>31d77ff</code></a> Added the release version</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/516ade166c0f33c6e5bcb0f57bebc58960d8dee8"><code>516ade1</code></a> Updated type annotations to match typeshed (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/77">#77</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/8b8791b662c0f62a574a09f305cd204dfb0a6a05"><code>8b8791b</code></a> Fixed bare <code>raise</code> and exception chaining when a handler raises an exception ...</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/0c94abe0f86fd134990d2a59ad84714e0d3f24d6"><code>0c94abe</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/75">#75</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/0878b8331a905f18b4d39b24b105b3e514ada65b"><code>0878b83</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/74">#74</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/fc578bcc6a05d9dbf129778c229f82b5b7bee8ea"><code>fc578bc</code></a> Switched to trusted publishing</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/4640be7afa4822e5803f4e09c5201d6669b0d2f8"><code>4640be7</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/73">#73</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/14bf3ed050af2998d0667aa59db306c46e774a64"><code>14bf3ed</code></a> Fixed erroneous TypeError in test_async_handler()</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/c97103955556d859493a2f4750fb9dddf8a9c9b3"><code>c971039</code></a> [pre-commit.ci] pre-commit autoupdate (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/72">#72</a>)</li> <li><a href="https://github.com/agronholm/exceptiongroup/commit/1d604fbe0f5f216bb7efa0ceb932745379e5a4f2"><code>1d604fb</code></a> Made catch() raise TypeError on async handler (<a href="https://redirect.github.com/agronholm/exceptiongroup/issues/69">#69</a>)</li> <li>Additional commits viewable in <a href="https://github.com/agronholm/exceptiongroup/compare/1.1.2...1.1.3">compare view</a></li> </ul> </details> [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=exceptiongroup&package-manager=pip&previous-version=1.1.2&new-version=1.1.3)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) You can trigger a rebase of this PR by commenting ``@dependabot` rebase`. 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andriilahuta added the type-bug An unexpected behavior, bug, or error label Apr 17, 2023

iritkatriel added a commit to iritkatriel/cpython that referenced this issue Apr 21, 2023

pythongh-103590: do not wrap a single exception raised from a try-exc…

17a1311

…ept*

iritkatriel mentioned this issue Apr 21, 2023

gh-103590: do not wrap a single exception raised from a try-except* #103665

Merged

iritkatriel closed this as completed in #103665 Apr 27, 2023

iritkatriel added a commit that referenced this issue Apr 27, 2023

gh-103590: do not wrap a single exception raised from a try-except* (#…

63842bd

…103665)

iritkatriel added a commit to iritkatriel/cpython that referenced this issue May 2, 2023

pythongh-103590: do not wrap a single exception raised from a try-exc…

2713e5a

…ept* (python#103665)

This was referenced May 2, 2023

[3.11] gh-103590: do not wrap a single exception raised from a try-except* #104094

Merged

gh-103590: mention that the change is included in 3.11.4 and clarify except* documentation #104095

Merged

iritkatriel added a commit that referenced this issue May 2, 2023

[3.11] gh-103590: do not wrap a single exception raised from a try-ex…

5386730

…cept* (#104094)

iritkatriel added a commit that referenced this issue May 3, 2023

gh-103590: mention that the change is included in 3.11.4 and clarify …

9f9e001

…except* documentation (#104095)

Zac-HD mentioned this issue Jul 2, 2023

test_catch_handler_raises regressed on 3.11.4 agronholm/exceptiongroup#64

Closed

Sep	OCT	Nov
	23
2022	2023	2024

[ExceptionGroup] Inconsistent raise inside except* #103590

[ExceptionGroup] Inconsistent raise inside except* #103590

andriilahuta commented Apr 17, 2023 •

edited by bedevere-bot

mdboom commented Apr 17, 2023

sunmy2019 commented Apr 17, 2023

andriilahuta commented Apr 17, 2023

carljm commented Apr 17, 2023 •

edited

iritkatriel commented Apr 21, 2023

[ExceptionGroup] Inconsistent raise inside except* #103590

[ExceptionGroup] Inconsistent raise inside except* #103590

Comments

andriilahuta commented Apr 17, 2023 • edited by bedevere-bot

Bug report

Your environment

Linked PRs

mdboom commented Apr 17, 2023

sunmy2019 commented Apr 17, 2023

andriilahuta commented Apr 17, 2023

carljm commented Apr 17, 2023 • edited

iritkatriel commented Apr 21, 2023

andriilahuta commented Apr 17, 2023 •

edited by bedevere-bot

carljm commented Apr 17, 2023 •

edited