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bpo-29587: Enable implicit exception chaining with gen.throw() by cjerdonek · Pull Request #19823 · python/cpython · GitHub
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bpo-29587: Enable implicit exception chaining with gen.throw()#19823

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cjerdonek merged 4 commits into
python:masterfrom
cjerdonek:fix-issue-29587-2
May 2, 2020
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bpo-29587: Enable implicit exception chaining with gen.throw()#19823
cjerdonek merged 4 commits into
python:masterfrom
cjerdonek:fix-issue-29587-2

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cjerdonek commented Apr 30, 2020 •
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This is a new version of PR #19811 to sort out the buildbot failures.

It enables implicit exception chaining when calling generator.throw(exc) by setting exc.__context__.

https://bugs.python.org/issue29587

Add a failing test for issue 29587.
e757c76
bpo-29587: set exc.__context__ when calling gen.throw() (pythonGH-19811) …
57597f2
Before this commit, if an exception was active inside a generator when calling gen.throw(), then that exception was lost (i.e. there was no implicit exception chaining). This commit fixes that.
cjerdonek requested a review from 1st1 as a code owner April 30, 2020 21:43
1st1 reviewed Apr 30, 2020
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vstinner requested changes Apr 30, 2020
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality Hide comment

test_unittest still crash on this PR. I tested on Linux (Fedora 32).

$ make clean $ make $ ./python -m test -v test_unittest (...) test_patch_nested_autospec_repr (unittest.test.testmock.testpatch.PatchTest) ... ok test_patch_object_keyword_args (unittest.test.testmock.testpatch.PatchTest) ... ok test_patch_object_with_spec_as_boolean (unittest.test.testmock.testpatch.PatchTest) ... ok test_patch_orderdict (unittest.test.testmock.testpatch.PatchTest) ... ok test_patch_propagates_exc_on_exit (unittest.test.testmock.testpatch.PatchTest) ... Fatal Python error: Segmentation fault Current thread 0x00007f886bd1c740 (most recent call first): File "/home/vstinner/python/master/Lib/unittest/mock.py", line 1524 in __exit__ File "/home/vstinner/python/master/Lib/unittest/test/testmock/testpatch.py", line 1673 in __exit__ File "/home/vstinner/python/master/Lib/contextlib.py", line 498 in __exit__ File "/home/vstinner/python/master/Lib/unittest/mock.py", line 1323 in decoration_helper File "/home/vstinner/python/master/Lib/contextlib.py", line 135 in __exit__ File "/home/vstinner/python/master/Lib/unittest/mock.py", line 1337 in patched File "/home/vstinner/python/master/Lib/unittest/case.py", line 201 in handle File "/home/vstinner/python/master/Lib/unittest/case.py", line 733 in assertRaises File "/home/vstinner/python/master/Lib/unittest/test/testmock/testpatch.py", line 1692 in test_patch_propagates_exc_on_exit (...)

bedevere-bot commented Apr 30, 2020

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When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

cjerdonek commented Apr 30, 2020

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Is there a way to mark this PR as "don't merge" for now? This is the same PR as before, so it has the same issue. The Azure CI job seems not to be running, which is what exhibited the failure before.

test_unittest still crash on this PR. I tested on Linux (Fedora 32).

Yes, this is the same failure as before. Everything passes locally on my Mac, so it will take me more time to look into this.

vstinner changed the title bpo-29587: Enable implicit exception chaining with gen.throw() [WIP] bpo-29587: Enable implicit exception chaining with gen.throw() Apr 30, 2020
vstinner marked this pull request as draft April 30, 2020 22:49

vstinner commented Apr 30, 2020 •
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Is there a way to mark this PR as "don't merge" for now?

Hum, I wasn't sure, so I did the 3 tricks that I know:

  • Add "do no merge label"
  • Add "[WIP]" in the PR title
  • Convert the PR to a draft

It seems like only the conversion to a draft technically prevents someone to merge the PR my mistake.

cjerdonek commented Apr 30, 2020

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Looks like that will cover it. ;)

cjerdonek commented May 1, 2020 •
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Okay, I believe my latest changes fix the buildbot failures from before.

Also, for future reference, below is a script I came up with that isolates the behavior difference between Mac and Fedora, with my prior version of the PR:

import re import sys def f(): exc, exc_value, tb = sys.exc_info() print(f'CLEARING FRAME: {tb.tb_frame!r}') tb.tb_frame.clear() def g(): # Uncommenting the following line caused the tb_frame.clear() line # above to exhibit the following platform-specific behavior: # 1) On Mac, this is logged to stderr # > TypeError: print_exception(): Exception expected for value, # NoneType found # 2) On Fedora 32, the following error happens: # > Fatal Python error: Segmentation fault data = re.compile('xxx') try: yield except Exception: f() gen = g() gen.send(None) gen.throw(ValueError)

Maybe this suggests an issue elsewhere in Python's code base.

Should this PR also get a What's New?

cjerdonek marked this pull request as ready for review May 1, 2020 08:43
cjerdonek changed the title [WIP] bpo-29587: Enable implicit exception chaining with gen.throw() bpo-29587: Enable implicit exception chaining with gen.throw() May 1, 2020

cjerdonek commented May 1, 2020

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I have made the requested changes; please review again.

bedevere-bot commented May 1, 2020

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Thanks for making the requested changes!

@vstinner: please review the changes made to this pull request.

bedevere-bot requested a review from vstinner May 1, 2020 08:47
vstinner approved these changes May 1, 2020
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LGTM. "./python -m test -j0 -r" does no longer crash on my Fedora.

I understood that passing NULL value to _PyErr_ChainExceptions() created the bug? Maybe add an assertion to prevent the situation to happen again?

cjerdonek commented May 1, 2020

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Thank you.

Regarding an assertion, the thing is that it looks like _PyErr_ChainExceptions() is designed to accept a NULL value. So maybe in the future it can be made to work. (That's why I added an XXX comment.) So I wouldn't want to add an assertion making it seem like it always has to be like that. It could just something about how things are set up right now that was causing the crash.

Would you still like me to add an assertion and/or perhaps a code comment explaining this possibility?

cjerdonek merged commit 0204726 into python:master May 2, 2020

bedevere-bot commented May 2, 2020

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@cjerdonek: Please replace # with GH- in the commit message next time. Thanks!

cjerdonek deleted the fix-issue-29587-2 branch May 2, 2020 01:16
This was referenced May 2, 2020
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cjerdonek added a commit that referenced this pull request May 3, 2020
bpo-29587: allow chaining NULL exceptions in _gen_throw() (GH-19877) …
21893fb
This is a follow-up to GH-19823 that removes the check that the exception value isn't NULL, prior to calling _PyErr_ChainExceptions(). This enables implicit exception chaining for gen.throw() in more circumstances. The commit also adds a test that a particular code snippet involving gen.throw() doesn't crash. The test shows why the new `gi_exc_state.exc_type != Py_None` check that was added is necessary. Without the new check, the code snippet (as well as a number of other tests) crashes on certain platforms (e.g. Fedora but not Mac).

cjerdonek commented May 3, 2020

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For future reference, I was able to remove the NULL check in a later PR (#19877): 21893fb

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