[Python-checkins] cpython (3.2): Issue #11647: allow contextmanager objects to be used as decorators as

Thu May 5 16:04:02 CEST 2011

http://hg.python.org/cpython/rev/e4ba097123f6
changeset: 69849:e4ba097123f6
branch: 3.2
parent: 69844:5a2d42a8c1ab
user: Nick Coghlan <ncoghlan at gmail.com>
date: Thu May 05 23:49:25 2011 +1000
summary:
 Issue #11647: allow contextmanager objects to be used as decorators as described in the docs. Initial patch by Ysj Ray.
files:
 Doc/library/contextlib.rst | 14 ++++++++++-
 Lib/contextlib.py | 28 +++++++++++++++++++++---
 Lib/test/test_contextlib.py | 7 +++++-
 Lib/test/test_with.py | 6 ++--
 Misc/ACKS | 1 +
 Misc/NEWS | 4 +++
 6 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -54,8 +54,12 @@
 the exception has been handled, and execution will resume with the statement
 immediately following the :keyword:`with` statement.
 
- contextmanager uses :class:`ContextDecorator` so the context managers it
- creates can be used as decorators as well as in :keyword:`with` statements.
+ :func:`contextmanager` uses :class:`ContextDecorator` so the context managers
+ it creates can be used as decorators as well as in :keyword:`with` statements.
+ When used as a decorator, a new generator instance is implicitly created on
+ each function call (this allows the otherwise "one-shot" context managers
+ created by :func:`contextmanager` to meet the requirement that context
+ managers support multiple invocations in order to be used as decorators).
 
 .. versionchanged:: 3.2
 Use of :class:`ContextDecorator`.
@@ -155,6 +159,12 @@
 def __exit__(self, *exc):
 return False
 
+ .. note::
+ As the decorated function must be able to be called multiple times, the
+ underlying context manager must support use in multiple :keyword:`with`
+ statements. If this is not the case, then the original construct with the
+ explicit :keyword:`with` statement inside the function should be used.
+
 .. versionadded:: 3.2
 
 
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -9,10 +9,23 @@
 
 class ContextDecorator(object):
 "A base class or mixin that enables context managers to work as decorators."
+
+ def _recreate_cm(self):
+ """Return a recreated instance of self.
+ 
+ Allows otherwise one-shot context managers like
+ _GeneratorContextManager to support use as
+ decorators via implicit recreation.
+ 
+ Note: this is a private interface just for _GCM in 3.2 but will be
+ renamed and documented for third party use in 3.3
+ """
+ return self
+
 def __call__(self, func):
 @wraps(func)
 def inner(*args, **kwds):
- with self:
+ with self._recreate_cm():
 return func(*args, **kwds)
 return inner
 
@@ -20,8 +33,15 @@
 class _GeneratorContextManager(ContextDecorator):
 """Helper for @contextmanager decorator."""
 
- def __init__(self, gen):
- self.gen = gen
+ def __init__(self, func, *args, **kwds):
+ self.gen = func(*args, **kwds)
+ self.func, self.args, self.kwds = func, args, kwds
+
+ def _recreate_cm(self):
+ # _GCM instances are one-shot context managers, so the
+ # CM must be recreated each time a decorated function is
+ # called
+ return self.__class__(self.func, *self.args, **self.kwds)
 
 def __enter__(self):
 try:
@@ -92,7 +112,7 @@
 """
 @wraps(func)
 def helper(*args, **kwds):
- return _GeneratorContextManager(func(*args, **kwds))
+ return _GeneratorContextManager(func, *args, **kwds)
 return helper
 
 
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -350,13 +350,13 @@
 
 
 def test_contextmanager_as_decorator(self):
- state = []
 @contextmanager
 def woohoo(y):
 state.append(y)
 yield
 state.append(999)
 
+ state = []
 @woohoo(1)
 def test(x):
 self.assertEqual(state, [1])
@@ -364,6 +364,11 @@
 test('something')
 self.assertEqual(state, [1, 'something', 999])
 
+ # Issue #11647: Ensure the decorated function is 'reusable'
+ state = []
+ test('something else')
+ self.assertEqual(state, [1, 'something else', 999])
+
 
 # This is needed to make the test actually run under regrtest.py!
 def test_main():
diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -14,8 +14,8 @@
 
 
 class MockContextManager(_GeneratorContextManager):
- def __init__(self, gen):
- _GeneratorContextManager.__init__(self, gen)
+ def __init__(self, func, *args, **kwds):
+ super().__init__(func, *args, **kwds)
 self.enter_called = False
 self.exit_called = False
 self.exit_args = None
@@ -33,7 +33,7 @@
 
 def mock_contextmanager(func):
 def helper(*args, **kwds):
- return MockContextManager(func(*args, **kwds))
+ return MockContextManager(func, *args, **kwds)
 return helper
 
 
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -704,6 +704,7 @@
 Brodie Rao
 Antti Rasinen
 Sridhar Ratnakumar
+Ysj Ray
 Eric Raymond
 Edward K. Ream
 Chris Rebert
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -83,6 +83,10 @@
 Library
 -------
 
+- Issue #11647: objects created using contextlib.contextmanager now support
+ more than one call to the function when used as a decorator. Initial patch
+ by Ysj Ray.
+
 - logging: don't define QueueListener if Python has no thread support.
 
 - functools.cmp_to_key() now works with collections.Hashable().
-- 
Repository URL: http://hg.python.org/cpython
