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| -rw-r--r-- | Doc/tutorial/classes.rst | 49 | ||||
| -rw-r--r-- | Doc/tutorial/errors.rst | 32 |
2 files changed, 31 insertions, 50 deletions
diff --git a/Doc/tutorial/classes.rst b/Doc/tutorial/classes.rst index 03b77e0..75c79d2 100644 --- a/Doc/tutorial/classes.rst +++ b/Doc/tutorial/classes.rst @@ -744,55 +744,6 @@ 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 diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst index 291fb4d..759588f 100644 --- a/Doc/tutorial/errors.rst +++ b/Doc/tutorial/errors.rst @@ -120,6 +120,33 @@ 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 @@ -219,7 +246,10 @@ exception to occur. For example:: 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 |