diff --git a/Doc/tutorial/classes.rst b/Doc/tutorial/classes.rst --- a/Doc/tutorial/classes.rst +++ b/Doc/tutorial/classes.rst @@ -739,65 +739,16 @@ data from a string buffer instead, and p or arithmetic operators, and assigning such a "pseudo-file" to sys.stdin will not cause the interpreter to read further input from it.) Instance method objects have attributes, too: ``m.__self__`` is the instance object with the method :meth:`m`, and ``m.__func__`` is the function object corresponding to the method. -.. _tut-exceptionclasses: - -Exceptions Are Classes Too -========================== - -User-defined exceptions are identified by classes as well. Using this mechanism -it is possible to create extensible hierarchies of exceptions. - -There are two new valid (semantic) forms for the :keyword:`raise` statement:: - - raise Class - - raise Instance - -In the first form, ``Class`` must be an instance of :class:`type` or of a -class derived from it. The first form is a shorthand for:: - - raise Class() - -A class in an :keyword:`except` clause is compatible with an exception if it is -the same class or a base class thereof (but not the other way around --- an -except clause listing a derived class is not compatible with a base class). For -example, the following code will print B, C, D in that order:: - - class B(Exception): - pass - class C(B): - pass - class D(C): - pass - - for cls in [B, C, D]: - try: - raise cls() - except D: - print("D") - except C: - print("C") - except B: - print("B") - -Note that if the except clauses were reversed (with ``except B`` first), it -would have printed B, B, B --- the first matching except clause is triggered. - -When an error message is printed for an unhandled exception, the exception's -class name is printed, then a colon and a space, and finally the instance -converted to a string using the built-in function :func:`str`. - - .. _tut-iterators: Iterators ========= By now you have probably noticed that most container objects can be looped over using a :keyword:`for` statement:: diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst --- a/Doc/tutorial/errors.rst +++ b/Doc/tutorial/errors.rst @@ -115,16 +115,43 @@ A :keyword:`try` statement may have more handlers for different exceptions. At most one handler will be executed. Handlers only handle exceptions that occur in the corresponding try clause, not in other handlers of the same :keyword:`try` statement. An except clause may name multiple exceptions as a parenthesized tuple, for example:: ... except (RuntimeError, TypeError, NameError): ... pass +A class in an :keyword:`except` clause is compatible with an exception if it is +the same class or a base class thereof (but not the other way around --- an +except clause listing a derived class is not compatible with a base class). For +example, the following code will print B, C, D in that order:: + + class B(Exception): + pass + + class C(B): + pass + + class D(C): + pass + + for cls in [B, C, D]: + try: + raise cls() + except D: + print("D") + except C: + print("C") + except B: + print("B") + +Note that if the except clauses were reversed (with ``except B`` first), it +would have printed B, B, B --- the first matching except clause is triggered. + The last except clause may omit the exception name(s), to serve as a wildcard. Use this with extreme caution, since it is easy to mask a real programming error in this way! It can also be used to print an error message and then re-raise the exception (allowing a caller to handle the exception as well):: import sys try: @@ -214,17 +241,20 @@ exception to occur. For example:: >>> raise NameError('HiThere') Traceback (most recent call last): File "", line 1, in ? NameError: HiThere The sole argument to :keyword:`raise` indicates the exception to be raised. This must be either an exception instance or an exception class (a class that -derives from :class:`Exception`). +derives from :class:`Exception`). If an exception class is passed, it will +be implicitly instantiated by calling its constructor with no arguments:: + + raise ValueError # shorthand for ``raise ValueError()`` If you need to determine whether an exception was raised but don't intend to handle it, a simpler form of the :keyword:`raise` statement allows you to re-raise the exception:: >>> try: ... raise NameError('HiThere') ... except NameError: