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| -rw-r--r-- | Doc/whatsnew/whatsnew25.tex | 62 |
1 files changed, 61 insertions, 1 deletions
diff --git a/Doc/whatsnew/whatsnew25.tex b/Doc/whatsnew/whatsnew25.tex index 3d048fd..8313c87 100644 --- a/Doc/whatsnew/whatsnew25.tex +++ b/Doc/whatsnew/whatsnew25.tex @@ -367,7 +367,65 @@ Sugalski.} %====================================================================== \section{PEP 352: Exceptions as New-Style Classes} -% XXX write this +Exception classes can now be new-style classes, not just classic classes, +and the built-in \exception{Exception} class and all + +The inheritance hierarchy for exceptions has been rearranged a bit. +In 2.5, the inheritance relationships are: + +\begin{verbatim} +BaseException # New in Python 2.5 +|- KeyboardInterrupt +|- SystemExit +|- Exception + |- (all other current built-in exceptions) +\end{verbatim} + +This rearrangement was done because people often want to catch all +exceptions that indicate program errors. \exception{KeyboardInterrupt} and +\exception{SystemExit} aren't errors, though, and usually represent an explicit +action such as the user hitting Control-C or code calling +\function{sys.exit()}. A bare \code{except:} will catch all exceptions, +so you commonly need to list \exception{KeyboardInterrupt} and +\exception{SystemExit} in order to re-raise them. The usual pattern is: + +\begin{verbatim} +try: + ... +except (KeyboardInterrupt, SystemExit): + raise +except: + # Log error... + # Continue running program... +\end{verbatim} + +In Python 2.5, you can now write \code{except Exception} to achieve +the same result, catching all the exceptions that usually indicate errors +but leaving \exception{KeyboardInterrupt} and +\exception{SystemExit} alone. As in previous versions, +a bare \code{except:} still catches all exceptions. + +The goal for Python 3.0 is to require any class raised as an exception +to derive from \exception{BaseException} or some descendant of +\exception{BaseException}, and future releases in the +Python 2.x series may begin to enforce this constraint. Therefore, I +suggest you begin making all your exception classes derive from +\exception{Exception} now. It's been suggested that the bare +\code{except:} form should be removed in Python 3.0, but Guido van~Rossum +hasn't decided whether to do this or not. + +Raising of strings as exceptions, as in the statement \code{raise +"Error occurred"}, is deprecated in Python 2.5 and will trigger a +warning. The aim is to be able to remove the string-exception feature +in a few releases. + + +\begin{seealso} + +\seepep{352}{}{PEP written by +Brett Cannon and Guido van Rossum; implemented by Brett Cannon.} + +\end{seealso} %====================================================================== @@ -454,6 +512,8 @@ details. \begin{itemize} +% ctypes added + % collections.deque now has .remove() % the cPickle module no longer accepts the deprecated None option in the |