diff options
Diffstat (limited to 'Doc/tutorial')
| -rw-r--r-- | Doc/tutorial/errors.rst | 28 |
1 files changed, 23 insertions, 5 deletions
diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst index 57919e3bad..67bb195566 100644 --- a/Doc/tutorial/errors.rst +++ b/Doc/tutorial/errors.rst @@ -284,8 +284,27 @@ 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 @@ -311,9 +330,8 @@ 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') |