bpo-25381: Update explanation of exceptions in C. #26838

terryjreedy · 2021-06-21T21:55:07Z

This paragraph in extending/extending.rst was unchanged (except for
NULL markup) since committed in 2007 Aug 15 for 2.6 alpha.
Except for there being 3 values, most details have changed.

https://bugs.python.org/issue25381

This paragraph in extending/extending.rst was unchanged (except for NULL markup) since committed in 2007 Aug 15 for 2.6 alpha.

gvanrossum · 2021-06-21T22:05:44Z

Doc/extending/extending.rst

+(usually a ``NULL`` pointer).  Exception information is stored in 3 static
+global variables inside the interpreter.  The first is the exception type,
+or ``NULL`` if no exception has occurred.  The second is the exception
+instance.  The third variable contains the stack


I'd write "three" in words instead of "3".

Technically these are not static global variables, they are members of the thread state nowadays.

If no exception occurred all three are none.

I think there are edge cases where the exception type is set but the instance is still NULL.

I also think the traceback may be NULL even though an exception is set (probably it's NULL until the exception bubbles into a Python frame.

'three', 'members', and 'all' done. Otherwise I'm going with the reference to sys.exc_info.

Doc/extending/extending.rst

iritkatriel · 2021-06-21T22:07:34Z

Doc/extending/extending.rst

-second global variable stores the "associated value" of the exception (the
-second argument to :keyword:`raise`).  A third variable contains the stack
+(usually a ``NULL`` pointer).  Exception information is stored in 3 static
+global variables inside the interpreter.  The first is the exception type,


Maybe "3 static global variables inside the interpreter" --> "3 fields on the interpreter's thread state" ?

Done, using 'members'.

I concur with @iritkatriel, they are not global variables. For example, you can two interpreters, each one has its own exception information.

@terryjreedy wrote "done", but the current PR stil says "3 static global variables".

iritkatriel · 2021-06-21T22:10:47Z

Doc/extending/extending.rst

+(usually a ``NULL`` pointer).  Exception information is stored in 3 static
+global variables inside the interpreter.  The first is the exception type,
+or ``NULL`` if no exception has occurred.  The second is the exception
+instance.  The third variable contains the stack
 traceback in case the error originated in Python code.  These three variables


it could originate in C but then go to python and get a traceback, no?

This is, actually, routine, as in IndexError originating in the C list code when executing, for instance, '[][1]'. So the author (apparently Georg Brandl) must have meant something else. I'm deleting the statement.

terryjreedy · 2021-06-22T00:07:03Z

The previous variable by variable discussion was mostly about relating the 3 variables to 2.x raise statements. No member by member discussion is needed now, so I deleted it. What the members might be while an exception is being processed by the interpreter is not relevant to users, certainly not for this entry.

Is there a entry that 'thread state' should be linked to?

Doc/extending/extending.rst

serhiy-storchaka · 2021-06-22T00:24:43Z

Doc/extending/extending.rst

-section on module :mod:`sys` in the Python Library Reference).  It is important
+(usually -1 or a ``NULL`` pointer).  Exception information is stored in
+three members of the interpreter's thread state.  These are ``NULL`` if
+there is no exception.  Otherwise they are the C equivalents of the members


Actually the second can be NULL or None and the third can be NULL in case of non-normalized exception.

The first is the exception type. NULL if no exception.

The second is either the instance of exception, or argument(s) which will be passed to exception constructor on normalization. NULL or None means no arguments. Tuple means several arguments. Otherwise it is a single argument.

The third is a traceback. Can be NULL for non-normalized exceptions.

See also PyErr_Fetch, PyErr_Restore and PyErr_NormalizeException. Terminology should be consistent.

Are you saying that a Python user of sys.exc_info might see these other value, or that the existing claim of C equivalents is incomplete? I presume the latter. If so, how about this, instead of These are....

If there is no exception, these are NULL. For a normalized exception , these are the C equivalents of the members of the Python tuple returned by :meth:sys.exc_info: the exception type, exception instance, and a traceback object. For a non-normalized exception, the second will be an argument or tuple of arguments that will be passed to the exception on normalization, or NULL or None, meaning "no arguments". The third argument may then be NULL.

This seems resolved now.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

github-actions · 2021-07-23T00:04:17Z

This PR is stale because it has been open for 30 days with no activity.

willingc · 2021-11-15T22:37:08Z

Doc/extending/extending.rst

-section on module :mod:`sys` in the Python Library Reference).  It is important
+(usually -1 or a ``NULL`` pointer).  Exception information is stored in
+three members of the interpreter's thread state.  These are ``NULL`` if
+there is no exception.  Otherwise they are the C equivalents of the members


This seems resolved now.

miss-islington · 2021-11-15T22:38:56Z

Thanks @terryjreedy for the PR, and @willingc for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

* bpo-25381: Update explanation of exception globals This paragraph in extending/extending.rst was unchanged (except for NULL markup) since committed in 2007 Aug 15 for 2.6 alpha. * Respond to reviews and remove duplication. * Update Doc/extending/extending.rst Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> (cherry picked from commit ad43dc0) Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

bedevere-bot · 2021-11-15T22:39:07Z

GH-29568 is a backport of this pull request to the 3.10 branch.

bedevere-bot · 2021-11-15T22:39:10Z

GH-29569 is a backport of this pull request to the 3.9 branch.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu> Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> (cherry picked from commit ad43dc0)

* bpo-25381: Update explanation of exception globals This paragraph in extending/extending.rst was unchanged (except for NULL markup) since committed in 2007 Aug 15 for 2.6 alpha. * Respond to reviews and remove duplication. * Update Doc/extending/extending.rst Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

bpo-25381: Update explanation of exception globals

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This paragraph in extending/extending.rst was unchanged (except for NULL markup) since committed in 2007 Aug 15 for 2.6 alpha.

terryjreedy added docs Documentation in the Doc dir needs backport to 3.9 only security fixes needs backport to 3.10 only security fixes labels Jun 21, 2021

terryjreedy requested review from iritkatriel, gvanrossum and serhiy-storchaka June 21, 2021 21:55

the-knights-who-say-ni added the CLA signed label Jun 21, 2021

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terryjreedy requested a review from vstinner June 21, 2021 22:17

Respond to reviews and remove duplication.

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Update Doc/extending/extending.rst

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Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

terryjreedy changed the title ~~bpo-25381: Update explanation of exception globals~~ bpo-25381: Update explanation of exceptions in C. Jun 22, 2021

github-actions bot added the stale Stale PR or inactive for long period of time. label Jul 23, 2021

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terryjreedy deleted the extend branch November 15, 2021 23:03

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bpo-25381: Update explanation of exceptions in C. #26838

bpo-25381: Update explanation of exceptions in C. #26838

terryjreedy commented Jun 21, 2021 •

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bpo-25381: Update explanation of exceptions in C. #26838

bpo-25381: Update explanation of exceptions in C. #26838

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