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Issue #15209: Fix typo and some additional wording tweaks

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Nick Coghlan 2012-12-09 16:21:46 +10:00
parent 3f7c0e4036
commit 0eee97cce6
1 changed files with 16 additions and 8 deletions
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24
Doc/library/exceptions.rst
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@ -39,19 +39,27 @@ When raising (or re-raising) an exception in an :keyword:`except` clause
new exception is not handled the traceback that is eventually displayed will new exception is not handled the traceback that is eventually displayed will
include the originating exception(s) and the final exception. include the originating exception(s) and the final exception.
When raising a new exception (rather than using to bare ``raise`` to re-raise When raising a new exception (rather than using a bare ``raise`` to re-raise
the exception currently being handled), the implicit exception chain can be the exception currently being handled), the implicit exception context can be
made explicit by using :keyword:`from` with :keyword:`raise`. The single supplemented with an explicit cause by using :keyword:`from` with
argument to :keyword:`from` must be an exception or ``None``. It will be set :keyword:`raise`::
as :attr:`__cause__` on the raised exception. Setting :attr:`__cause__`
also implicitly sets the :attr:`__suppress_context__` attribute to raise new_exc from original_exc
``True``.
The expression following :keyword:`from` must be an exception or ``None``. It
will be set as :attr:`__cause__` on the raised exception. Setting
:attr:`__cause__` also implicitly sets the :attr:`__suppress_context__`
attribute to ``True``, so that using ``raise new_exc from None``
effectively replaces the old exception with the new one for display
purposes (e.g. converting :exc:`KeyError` to :exc:`AttributeError`, while
leaving the old exception available in :attr:`__context__` for introspection
when debugging.
The default traceback display code shows these chained exceptions in The default traceback display code shows these chained exceptions in
addition to the traceback for the exception itself. An explicitly chained addition to the traceback for the exception itself. An explicitly chained
exception in :attr:`__cause__` is always shown when present. An implicitly exception in :attr:`__cause__` is always shown when present. An implicitly
chained exception in :attr:`__context__` is shown only if :attr:`__cause__` chained exception in :attr:`__context__` is shown only if :attr:`__cause__`
is not set and :attr:`__suppress_context__` is false. is :const:`None` and :attr:`__suppress_context__` is false.
In either case, the exception itself is always shown after any chained In either case, the exception itself is always shown after any chained
exceptions so that the final line of the traceback always shows the last exceptions so that the final line of the traceback always shows the last