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Removed contextlib.nested()

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Raymond Hettinger 2009-07-01 01:32:12 +00:00
parent 6e5b0a1140
commit 9c4d0edd64
3 changed files with 0 additions and 216 deletions
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49
Doc/library/contextlib.rst
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@ -52,55 +52,6 @@ Functions provided:
immediately following the :keyword:`with` statement. 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) .. function:: closing(thing)
Return a context manager that closes *thing* upon completion of the block. This Return a context manager that closes *thing* upon completion of the block. This

45
Lib/contextlib.py
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@ -85,51 +85,6 @@ def contextmanager(func):
return helper return helper
@contextmanager
def nested(*managers):
"""Combine multiple context managers into a single nested context manager.
This function has been deprecated in favour of the multiple manager form
of the with statement.
The one advantage of this function over the multiple manager form of the
with statement is that argument unpacking allows it to be
used with a variable number of context managers as follows:
with nested(*managers):
do_something()
"""
warn("With-statements now directly support multiple context managers",
DeprecationWarning, 3)
exits = []
vars = []
exc = (None, None, None)
try:
for mgr in managers:
exit = mgr.__exit__
enter = mgr.__enter__
vars.append(enter())
exits.append(exit)
yield vars
except:
exc = sys.exc_info()
finally:
while exits:
exit = exits.pop()
try:
if exit(*exc):
exc = (None, None, None)
except:
exc = sys.exc_info()
if exc != (None, None, None):
# Don't rely on sys.exc_info() still containing
# the right information. Another exception may
# have been raised and caught by an exit method
# exc[1] already has the __traceback__ attribute populated
raise exc[1]
class closing(object): class closing(object):
"""Context to automatically close something at the end of a block. """Context to automatically close something at the end of a block.

122
Lib/test/test_contextlib.py
View file

@ -101,128 +101,6 @@ class ContextManagerTestCase(unittest.TestCase):
self.assertEqual(baz.foo, 'bar') self.assertEqual(baz.foo, 'bar')
self.assertEqual(baz.__doc__, "Whee!") self.assertEqual(baz.__doc__, "Whee!")
class NestedTestCase(unittest.TestCase):
# XXX This needs more work
def test_nested(self):
@contextmanager
def a():
yield 1
@contextmanager
def b():
yield 2
@contextmanager
def c():
yield 3
with nested(a(), b(), c()) as (x, y, z):
self.assertEqual(x, 1)
self.assertEqual(y, 2)
self.assertEqual(z, 3)
def test_nested_cleanup(self):
state = []
@contextmanager
def a():
state.append(1)
try:
yield 2
finally:
state.append(3)
@contextmanager
def b():
state.append(4)
try:
yield 5
finally:
state.append(6)
try:
with nested(a(), b()) as (x, y):
state.append(x)
state.append(y)
1/0
except ZeroDivisionError:
self.assertEqual(state, [1, 4, 2, 5, 6, 3])
else:
self.fail("Didn't raise ZeroDivisionError")
def test_nested_right_exception(self):
state = []
@contextmanager
def a():
yield 1
class b(object):
def __enter__(self):
return 2
def __exit__(self, *exc_info):
try:
raise Exception()
except:
pass
try:
with nested(a(), b()) as (x, y):
1/0
except ZeroDivisionError:
self.assertEqual((x, y), (1, 2))
except Exception:
self.fail("Reraised wrong exception")
else:
self.fail("Didn't raise ZeroDivisionError")
def test_nested_b_swallows(self):
@contextmanager
def a():
yield
@contextmanager
def b():
try:
yield
except:
# Swallow the exception
pass
try:
with nested(a(), b()):
1/0
except ZeroDivisionError:
self.fail("Didn't swallow ZeroDivisionError")
def test_nested_break(self):
@contextmanager
def a():
yield
state = 0
while True:
state += 1
with nested(a(), a()):
break
state += 10
self.assertEqual(state, 1)
def test_nested_continue(self):
@contextmanager
def a():
yield
state = 0
while state < 3:
state += 1
with nested(a(), a()):
continue
state += 10
self.assertEqual(state, 3)
def test_nested_return(self):
@contextmanager
def a():
try:
yield
except:
pass
def foo():
with nested(a(), a()):
return 1
return 10
self.assertEqual(foo(), 1)
class ClosingTestCase(unittest.TestCase): class ClosingTestCase(unittest.TestCase):
# XXX This needs more work # XXX This needs more work