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bpo-42179: Clarify exception chaining #23160

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willingc merged 5 commits into from
Dec 16, 2020
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bpo-42179: Clarify exception chaining #23160

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86fe587
Update errors.rst
greatvovan Nov 5, 2020
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greatvovan Nov 5, 2020
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greatvovan Nov 5, 2020
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Merge branch 'master' into bugfix/bpo-42179
greatvovan Nov 6, 2020
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greatvovan Nov 9, 2020
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Update errors.rst 
Clarify exception chaining behaviour and give a reference to the library documentation.
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greatvovan authored Nov 5, 2020
commit 86fe587f02a2bd317c9c92b567649b192bca91b1
9 changes: 7 additions & 2 deletions Doc/tutorial/errors.rst
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Expand Up @@ -301,8 +301,13 @@ This can be useful when you are transforming exceptions. For example::

The expression following the :keyword:`from` must be either an exception or
``None``. Exception chaining happens automatically when an exception is raised
inside an exception handler or :keyword:`finally` section. Exception chaining
can be disabled by using ``from None`` idiom:
inside an exception handler or :keyword:`finally` section, however in this case
``__context__`` attribute of the exception is used. Chaining with
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@willingc willingc Nov 5, 2020

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I recommend submitting this sentence right before the builtin exceptions sentence after #23162 lands. Then add "Chaining with ... takes priority."

``__context__`` works similarly, but when formatting exception traceback
``__cause__`` takes priority. For more information about chaining mechanics
see :ref:`bltin-exceptions`.

Exception chaining can be disabled by using ``from None`` idiom:

>>> try:
... open('database.sqlite')
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