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| -rw-r--r-- | Doc/library/contextlib.rst | 49 |
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diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst index ca37f0f..2ee9e8d 100644 --- a/Doc/library/contextlib.rst +++ b/Doc/library/contextlib.rst @@ -52,55 +52,6 @@ Functions provided: immediately following the :keyword:`with` statement. -.. function:: nested(mgr1[, mgr2[, ...]]) - - Combine multiple context managers into a single nested context manager. - - This function has been deprecated in favour of the multiple manager form - of the :keyword:`with` statement. - - The one advantage of this function over the multiple manager form of the - :keyword:`with` statement is that argument unpacking allows it to be - used with a variable number of context managers as follows:: - - from contextlib import nested - - with nested(*managers): - do_something() - - Note that if the :meth:`__exit__` method of one of the nested context managers - indicates an exception should be suppressed, no exception information will be - passed to any remaining outer context managers. Similarly, if the - :meth:`__exit__` method of one of the nested managers raises an exception, any - previous exception state will be lost; the new exception will be passed to the - :meth:`__exit__` methods of any remaining outer context managers. In general, - :meth:`__exit__` methods should avoid raising exceptions, and in particular they - should not re-raise a passed-in exception. - - This function has two major quirks that have led to it being deprecated. Firstly, - as the context managers are all constructed before the function is invoked, the - :meth:`__new__` and :meth:`__init__` methods of the inner context managers are - not actually covered by the scope of the outer context managers. That means, for - example, that using :func:`nested` to open two files is a programming error as the - first file will not be closed promptly if an exception is thrown when opening - the second file. - - Secondly, if the :meth:`__enter__` method of one of the inner context managers - raises an exception that is caught and suppressed by the :meth:`__exit__` method - of one of the outer context managers, this construct will raise - :exc:`RuntimeError` rather than skipping the body of the :keyword:`with` - statement. - - Developers that need to support nesting of a variable number of context managers - can either use the :mod:`warnings` module to suppress the DeprecationWarning - raised by this function or else use this function as a model for an application - specific implementation. - - .. deprecated:: 3.1 - The with-statement now supports this functionality directly (without the - confusing error prone quirks). - - .. function:: closing(thing) Return a context manager that closes *thing* upon completion of the block. This |