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gh-119786: move a few more details on exception handling from devguide to InternalDocs (#124989)

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Irit Katriel 2024-10-05 00:48:12 +01:00 committed by GitHub
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@ -75,7 +75,8 @@ table. If it finds a handler, control flow transfers to it. Otherwise, the
exception bubbles up to the caller, and the caller's frame is
checked for a handler covering the `CALL` instruction. This
repeats until a handler is found or the topmost frame is reached.
If no handler is found, the program terminates. During unwinding,
If no handler is found, then the interpreter function
(``_PyEval_EvalFrameDefault()``) returns NULL. During unwinding,
the traceback is constructed as each frame is added to it by
``PyTraceBack_Here()``, which is in
[Python/traceback.c](https://github.com/python/cpython/blob/main/Python/traceback.c).
@ -182,3 +183,12 @@ The interpreter's function to lookup the table by instruction offset is
The Python function ``_parse_exception_table()`` in
[Lib/dis.py](https://github.com/python/cpython/blob/main/Lib/dis.py)
returns the exception table content as a list of namedtuple instances.
Exception Chaining Implementation
---------------------------------
[Exception chaining](https://docs.python.org/dev/tutorial/errors.html#exception-chaining)
refers to setting the ``__context__`` and ``__cause__`` fields of an exception as it is
being raised. The ``__context__`` field is set by ``_PyErr_SetObject()`` in
:cpy-file:`Python/errors.c` (which is ultimately called by all ``PyErr_Set*()`` functions).
The ``__cause__`` field (explicit chaining) is set by the ``RAISE_VARARGS`` bytecode.