From 0cc27417f2cd399c432d7dda9aeca1d81af76936 Mon Sep 17 00:00:00 2001 From: toonarmycaptain Date: Wed, 11 Sep 2019 10:37:13 -0500 Subject: [PATCH] Improve clarity of try-return-finally-return (GH-15677) Clarify execution in try-return-finally-return case. --- Doc/tutorial/errors.rst | 31 ++++++++++++++++++++++--------- Misc/ACKS | 1 + 2 files changed, 23 insertions(+), 9 deletions(-) diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst index e9a63e42527..75a49259d44 100644 --- a/Doc/tutorial/errors.rst +++ b/Doc/tutorial/errors.rst @@ -388,15 +388,28 @@ example:: File "", line 2, in KeyboardInterrupt -A *finally clause* is always executed before leaving the :keyword:`try` -statement, whether an exception has occurred or not. When an exception has -occurred in the :keyword:`!try` clause and has not been handled by an -:keyword:`except` clause (or it has occurred in an :keyword:`!except` or -:keyword:`!else` clause), it is re-raised after the :keyword:`finally` clause has -been executed. The :keyword:`!finally` clause is also executed "on the way out" -when any other clause of the :keyword:`!try` statement is left via a -:keyword:`break`, :keyword:`continue` or :keyword:`return` statement. A more -complicated example:: +If a :keyword:`finally` clause is present, the :keyword:`finally` clause will execute as the last task before the :keyword:`try` statement completes. The :keyword:`finally` clause runs whether or not the :keyword:`try` statement produces an exception. The following points discuss more complex cases when an exception occurs: + +* If an exception occurs during execution of the :keyword:`!try` clause, the exception may be handled by an :keyword:`except` clause. In all cases, the exception is re-raised after the :keyword:`!finally` clause has been executed. + +* An exception could occur during execution of an :keyword:`!except` or :keyword:`!else` clause. Again, the exception is re-raised after the :keyword:`!finally` clause has been executed. + +* If the :keyword:`!try` statement reaches a :keyword:`break`, :keyword:`continue` or :keyword:`return` statement, the :keyword:`finally` clause will execute just prior to the :keyword:`break`, :keyword:`continue` or :keyword:`return` statement's execution. + +* If a :keyword:`finally` clause includes a :keyword:`return` statement, the :keyword:`finally` clause's :keyword:`return` statement will execute before, and instead of, the :keyword:`return` statement in a :keyword:`try` clause. + +For example:: + + >>> def bool_return(): -> bool: + ... try: + ... return True + ... finally: + ... return False + ... + >>> bool_return() + False + +A more complicated example:: >>> def divide(x, y): ... try: diff --git a/Misc/ACKS b/Misc/ACKS index d37d2bdcc43..f321131b2ab 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -58,6 +58,7 @@ Jon Anglin Michele Angrisano Ankur Ankan Heidi Annexstad +David Antonini Ramchandra Apte Éric Araujo Alexandru Ardelean