[Python-checkins] [3.10] gh-97654: Add auto exception chaining example to tutorial (GH-97703) (#97884)
ambv
webhook-mailer at python.org
Wed Oct 5 17:51:16 EDT 2022
https://github.com/python/cpython/commit/9f1c9b1a7a04513fcc8a679fb1075701f37ab621
commit: 9f1c9b1a7a04513fcc8a679fb1075701f37ab621
branch: 3.10
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2022-10-05T14:51:10-07:00
summary:
[3.10] gh-97654: Add auto exception chaining example to tutorial (GH-97703) (#97884)
Add auto exception chaining example to tutorial
(cherry picked from commit 395b66a0ae5237eec195ca97daaaf8563706ed34)
Co-authored-by: Shahriar Heidrich <smheidrich at weltenfunktion.de>
files:
M Doc/tutorial/errors.rst
diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst
index 3f09db210406..ecfb61288390 100644
--- a/Doc/tutorial/errors.rst
+++ b/Doc/tutorial/errors.rst
@@ -275,8 +275,27 @@ re-raise the exception::
Exception Chaining
==================
-The :keyword:`raise` statement allows an optional :keyword:`from<raise>` which enables
-chaining exceptions. For example::
+If an unhandled exception occurs inside an :keyword:`except` section, it will
+have the exception being handled attached to it and included in the error
+message::
+
+ >>> try:
+ ... open("database.sqlite")
+ ... except OSError:
+ ... raise RuntimeError("unable to handle error")
+ ...
+ Traceback (most recent call last):
+ File "<stdin>", line 2, in <module>
+ FileNotFoundError: [Errno 2] No such file or directory: 'database.sqlite'
+ <BLANKLINE>
+ During handling of the above exception, another exception occurred:
+ <BLANKLINE>
+ Traceback (most recent call last):
+ File "<stdin>", line 4, in <module>
+ RuntimeError: unable to handle error
+
+To indicate that an exception is a direct consequence of another, the
+:keyword:`raise` statement allows an optional :keyword:`from<raise>` clause::
# exc must be exception instance or None.
raise RuntimeError from exc
@@ -302,9 +321,8 @@ This can be useful when you are transforming exceptions. For example::
File "<stdin>", line 4, in <module>
RuntimeError: Failed to open database
-Exception chaining happens automatically when an exception is raised inside an
-:keyword:`except` or :keyword:`finally` section. This can be
-disabled by using ``from None`` idiom:
+It also allows disabling automatic exception chaining using the ``from None``
+idiom::
>>> try:
... open('database.sqlite')
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