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Removed contextlib.nested()

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Raymond Hettinger 2009-07-01 01:32:12 +00:00
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Doc/library/contextlib.rst
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@ -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