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| author | Nick Coghlan <ncoghlan@gmail.com> | 2012-02-26 07:49:52 (GMT) |
|---|---|---|
| committer | Nick Coghlan <ncoghlan@gmail.com> | 2012-02-26 07:49:52 (GMT) |
| commit | ab7bf2143e67ddc1510413fa0d7f9c621adf22fa (patch) | |
| tree | 62a24ed4f57e4db638ebde745bb83e2e09fc86e3 /Doc/library | |
| parent | cda6b6d60d96e6f755da92deb5e4066839095791 (diff) | |
| download | cpython-ab7bf2143e67ddc1510413fa0d7f9c621adf22fa.zip cpython-ab7bf2143e67ddc1510413fa0d7f9c621adf22fa.tar.gz cpython-ab7bf2143e67ddc1510413fa0d7f9c621adf22fa.tar.bz2 | |
Close issue #6210: Implement PEP 409
Diffstat (limited to 'Doc/library')
| -rw-r--r-- | Doc/library/exceptions.rst | 18 | ||||
| -rw-r--r-- | Doc/library/stdtypes.rst | 9 |
2 files changed, 23 insertions, 4 deletions
diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst index 3f1a30d..7e3a0c3 100644 --- a/Doc/library/exceptions.rst +++ b/Doc/library/exceptions.rst @@ -34,6 +34,24 @@ programmers are encouraged to at least derive new exceptions from the defining exceptions is available in the Python Tutorial under :ref:`tut-userexceptions`. +When raising (or re-raising) an exception in an :keyword:`except` clause +:attr:`__context__` is automatically set to the last exception caught; if the +new exception is not handled the traceback that is eventually displayed will +include the originating exception(s) and the final exception. + +This implicit exception chain can be made explicit by using :keyword:`from` +with :keyword:`raise`. The single argument to :keyword:`from` must be an +exception or :const:`None`, and it will bet set as :attr:`__cause__` on the +raised exception. If :attr:`__cause__` is an exception it will be displayed +instead of :attr:`__context__`; if :attr:`__cause__` is None, +:attr:`__context__` will not be displayed by the default exception handling +code. (Note: the default value for :attr:`__context__` is :const:`None`, +while the default value for :attr:`__cause__` is :const:`Ellipsis`.) + +In either case, the default exception handling code will not display +any of the remaining links in the :attr:`__context__` chain if +:attr:`__cause__` has been set. + Base classes ------------ diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst index be06595..1526a0a 100644 --- a/Doc/library/stdtypes.rst +++ b/Doc/library/stdtypes.rst @@ -2985,10 +2985,11 @@ It is written as ``None``. The Ellipsis Object ------------------- -This object is commonly used by slicing (see :ref:`slicings`). It supports no -special operations. There is exactly one ellipsis object, named -:const:`Ellipsis` (a built-in name). ``type(Ellipsis)()`` produces the -:const:`Ellipsis` singleton. +This object is commonly used by slicing (see :ref:`slicings`), but may also +be used in other situations where a sentinel value other than :const:`None` +is needed. It supports no special operations. There is exactly one ellipsis +object, named :const:`Ellipsis` (a built-in name). ``type(Ellipsis)()`` +produces the :const:`Ellipsis` singleton. It is written as ``Ellipsis`` or ``...``. |