def __init__(self, func, *args, **kwds):
self.gen = func(*args, **kwds)
self.func, self.args, self.kwds = func, args, kwds
+ # Issue 19330: ensure context manager instances have good docstrings
+ doc = getattr(func, "__doc__", None)
+ if doc is None:
+ doc = type(self).__doc__
+ self.__doc__ = doc
+ # Unfortunately, this still doesn't provide good help output when
+ # inspecting the created context manager instances, since pydoc
+ # currently bypasses the instance docstring and shows the docstring
+ # for the class instead.
+ # See http://bugs.python.org/issue19404 for more details.
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
return helper
-# Unfortunately, this was originally published as a class, so
-# backwards compatibility prevents the use of the wrapper function
-# approach used for the other classes
class closing(object):
"""Context to automatically close something at the end of a block.
def __exit__(self, *exc_info):
self.thing.close()
-class _RedirectStdout:
- """Helper for redirect_stdout."""
+class redirect_stdout:
+ """Context manager for temporarily redirecting stdout to another file
+
+ # How to send help() to stderr
+ with redirect_stdout(sys.stderr):
+ help(dir)
+
+ # How to write help() to a file
+ with open('help.txt', 'w') as f:
+ with redirect_stdout(f):
+ help(pow)
+ """
def __init__(self, new_target):
self._new_target = new_target
self._old_target = self._sentinel
sys.stdout = restore_stdout
-# Use a wrapper function since we don't care about supporting inheritance
-# and a function gives much cleaner output in help()
-def redirect_stdout(target):
- """Context manager for temporarily redirecting stdout to another file
- # How to send help() to stderr
- with redirect_stdout(sys.stderr):
- help(dir)
- # How to write help() to a file
- with open('help.txt', 'w') as f:
- with redirect_stdout(f):
- help(pow)
- """
- return _RedirectStdout(target)
+class suppress:
+ """Context manager to suppress specified exceptions
+
+ After the exception is suppressed, execution proceeds with the next
+ statement following the with statement.
+ with suppress(FileNotFoundError):
+ os.remove(somefile)
+ # Execution still resumes here if the file was already removed
+ """
-class _SuppressExceptions:
- """Helper for suppress."""
def __init__(self, *exceptions):
self._exceptions = exceptions
pass
def __exit__(self, exctype, excinst, exctb):
- # Unlike isinstance and issubclass, exception handling only
- # looks at the concrete type heirarchy (ignoring the instance
- # and subclass checking hooks). However, all exceptions are
- # also required to be concrete subclasses of BaseException, so
- # if there's a discrepancy in behaviour, we currently consider it
- # the fault of the strange way the exception has been defined rather
- # than the fact that issubclass can be customised while the
- # exception checks can't.
+ # Unlike isinstance and issubclass, CPython exception handling
+ # currently only looks at the concrete type hierarchy (ignoring
+ # the instance and subclass checking hooks). While Guido considers
+ # that a bug rather than a feature, it's a fairly hard one to fix
+ # due to various internal implementation details. suppress provides
+ # the simpler issubclass based semantics, rather than trying to
+ # exactly reproduce the limitations of the CPython interpreter.
+ #
# See http://bugs.python.org/issue12029 for more details
return exctype is not None and issubclass(exctype, self._exceptions)
-# Use a wrapper function since we don't care about supporting inheritance
-# and a function gives much cleaner output in help()
-def suppress(*exceptions):
- """Context manager to suppress specified exceptions
-
- After the exception is suppressed, execution proceeds with the next
- statement following the with statement.
-
- with suppress(FileNotFoundError):
- os.remove(somefile)
- # Execution still resumes here if the file was already removed
- """
- return _SuppressExceptions(*exceptions)
# Inspired by discussions on http://bugs.python.org/issue13585
class ExitStack(object):
class ContextManagerTestCase(unittest.TestCase):
+ def test_instance_docstring_given_function_docstring(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ # See http://bugs.python.org/issue19404 for why this doesn't currently
+ # affect help() output :(
+ def gen_with_docstring():
+ """This has a docstring"""
+ yield
+ gen_docstring = gen_with_docstring.__doc__
+ cm_with_docstring = contextmanager(gen_with_docstring)
+ self.assertEqual(cm_with_docstring.__doc__, gen_docstring)
+ obj = cm_with_docstring()
+ self.assertEqual(obj.__doc__, gen_docstring)
+ self.assertNotEqual(obj.__doc__, type(obj).__doc__)
+
def test_contextmanager_plain(self):
state = []
@contextmanager
class ClosingTestCase(unittest.TestCase):
- # XXX This needs more work
+ def test_instance_docs(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ cm_docstring = closing.__doc__
+ obj = closing(None)
+ self.assertEqual(obj.__doc__, cm_docstring)
def test_closing(self):
state = []
class mycontext(ContextDecorator):
+ """Example decoration-compatible context manager for testing"""
started = False
exc = None
catch = False
class TestContextDecorator(unittest.TestCase):
+ def test_instance_docs(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ cm_docstring = mycontext.__doc__
+ obj = mycontext()
+ self.assertEqual(obj.__doc__, cm_docstring)
+
def test_contextdecorator(self):
context = mycontext()
with context as result:
class TestExitStack(unittest.TestCase):
+ def test_instance_docs(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ cm_docstring = ExitStack.__doc__
+ obj = ExitStack()
+ self.assertEqual(obj.__doc__, cm_docstring)
+
def test_no_resources(self):
with ExitStack():
pass
class TestRedirectStdout(unittest.TestCase):
+ def test_instance_docs(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ cm_docstring = redirect_stdout.__doc__
+ obj = redirect_stdout(None)
+ self.assertEqual(obj.__doc__, cm_docstring)
+
def test_redirect_to_string_io(self):
f = io.StringIO()
msg = "Consider an API like help(), which prints directly to stdout"
class TestSuppress(unittest.TestCase):
+ def test_instance_docs(self):
+ # Issue 19330: ensure context manager instances have good docstrings
+ cm_docstring = suppress.__doc__
+ obj = suppress()
+ self.assertEqual(obj.__doc__, cm_docstring)
+
def test_no_result_from_enter(self):
with suppress(ValueError) as enter_result:
self.assertIsNone(enter_result)
with suppress(TypeError):
len(5)
+ def test_exception_hierarchy(self):
+ with suppress(LookupError):
+ 'Hello'[50]
+
+ def test_other_exception(self):
+ with self.assertRaises(ZeroDivisionError):
+ with suppress(TypeError):
+ 1/0
+
+ def test_no_args(self):
+ with self.assertRaises(ZeroDivisionError):
+ with suppress():
+ 1/0
+
def test_multiple_exception_args(self):
with suppress(ZeroDivisionError, TypeError):
1/0
with suppress(ZeroDivisionError, TypeError):
len(5)
- def test_exception_hierarchy(self):
- with suppress(LookupError):
- 'Hello'[50]
-
def test_cm_is_reentrant(self):
ignore_exceptions = suppress(Exception)
with ignore_exceptions:
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