Merge from default

.hgignore

@@ -15,3 +15,4 @@ htmlcov/
 _build/
 dist/
 MANIFEST
+.tox

NEWS.rst

@@ -1,6 +1,19 @@
 Release History
 ---------------
 
+0.5.0 (2016-01-12)
+~~~~~~~~~~~~~~~~~~
+
+* Updated to include all features from the Python 3.4 and 3.5 releases of
+  contextlib (also includes some ``ExitStack`` enhancements made following
+  the integration into the standard library for Python 3.3)
+
+* The legacy ``ContextStack`` and ``ContextDecorator.refresh_cm`` APIs are
+  no longer documented
+
+* Python 2.6, 3.2 and 3.3 have been dropped from compatibility testing
+
+
 0.4.0 (2012-05-05)
 ~~~~~~~~~~~~~~~~~~
 

VERSION.txt

@@ -1 +1 @@
-0.4.0
+0.5.0

contextlib2.py

@@ -1,12 +1,15 @@
 """contextlib2 - backports and enhancements to the contextlib module"""
 
 import sys
+import warnings
 from collections import deque
 from functools import wraps
 
-__all__ = ["contextmanager", "closing", "ContextDecorator",
+__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
-           "ContextStack", "ExitStack"]
+           "redirect_stdout", "redirect_stderr", "suppress"]
 
+# Backwards compatibility
+__all__ += ["ContextStack"]
 
 class ContextDecorator(object):
     "A base class or mixin that enables context managers to work as decorators."
@@ -20,13 +23,30 @@ class ContextDecorator(object):
         Overriding this method allows otherwise one-shot context managers
         like _GeneratorContextManager to support use as decorators via
         implicit recreation.
+
+        DEPRECATED: refresh_cm was never added to the standard library's
+                    ContextDecorator API
+        """
+        warnings.warn("refresh_cm was never added to the standard library",
+                      DeprecationWarning)
+        return self._recreate_cm()
+
+    def _recreate_cm(self):
+        """Return a recreated instance of self.
+
+        Allows an otherwise one-shot context manager like
+        _GeneratorContextManager to support use as
+        a decorator via implicit recreation.
+
+        This is a private interface just for _GeneratorContextManager.
+        See issue #11647 for details.
         """
         return self
 
     def __call__(self, func):
         @wraps(func)
         def inner(*args, **kwds):
-            with self.refresh_cm():
+            with self._recreate_cm():
                 return func(*args, **kwds)
         return inner
 
@@ -34,15 +54,25 @@ class ContextDecorator(object):
 class _GeneratorContextManager(ContextDecorator):
     """Helper for @contextmanager decorator."""
 
-    def __init__(self, func, *args, **kwds):
+    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 refresh_cm(self):
+    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)
+        return self.__class__(self.func, self.args, self.kwds)
 
     def __enter__(self):
         try:
@@ -67,10 +97,17 @@ class _GeneratorContextManager(ContextDecorator):
                 self.gen.throw(type, value, traceback)
                 raise RuntimeError("generator didn't stop after throw()")
             except StopIteration as exc:
-                # Suppress the exception *unless* it's the same exception that
+                # Suppress StopIteration *unless* it's the same exception that
                 # was passed to throw().  This prevents a StopIteration
-                # raised inside the "with" statement from being suppressed
+                # raised inside the "with" statement from being suppressed.
                 return exc is not value
+            except RuntimeError as exc:
+                # Likewise, avoid suppressing if a StopIteration exception
+                # was passed to throw() and later wrapped into a RuntimeError
+                # (see PEP 479).
+                if _HAVE_EXCEPTION_CHAINING and exc.__cause__ is value:
+                    return False
+                raise
             except:
                 # only re-raise if it's *not* the exception that was
                 # passed to throw(), because __exit__() must not raise
@@ -113,7 +150,7 @@ def contextmanager(func):
     """
     @wraps(func)
     def helper(*args, **kwds):
-        return _GeneratorContextManager(func, *args, **kwds)
+        return _GeneratorContextManager(func, args, kwds)
     return helper
 
 
@@ -142,6 +179,115 @@ class closing(object):
         self.thing.close()
 
 
+class _RedirectStream:
+
+    _stream = None
+
+    def __init__(self, new_target):
+        self._new_target = new_target
+        # We use a list of old targets to make this CM re-entrant
+        self._old_targets = []
+
+    def __enter__(self):
+        self._old_targets.append(getattr(sys, self._stream))
+        setattr(sys, self._stream, self._new_target)
+        return self._new_target
+
+    def __exit__(self, exctype, excinst, exctb):
+        setattr(sys, self._stream, self._old_targets.pop())
+
+
+class redirect_stdout(_RedirectStream):
+    """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)
+    """
+
+    _stream = "stdout"
+
+
+class redirect_stderr(_RedirectStream):
+    """Context manager for temporarily redirecting stderr to another file."""
+
+    _stream = "stderr"
+
+
+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
+    """
+
+    def __init__(self, *exceptions):
+        self._exceptions = exceptions
+
+    def __enter__(self):
+        pass
+
+    def __exit__(self, exctype, excinst, exctb):
+        # 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)
+
+
+# Context manipulation is Python 3 only
+_HAVE_EXCEPTION_CHAINING = sys.version_info.major >= 3
+if _HAVE_EXCEPTION_CHAINING:
+    def _make_context_fixer(frame_exc):
+        def _fix_exception_context(new_exc, old_exc):
+            # Context may not be correct, so find the end of the chain
+            while 1:
+                exc_context = new_exc.__context__
+                if exc_context is old_exc:
+                    # Context is already set correctly (see issue 20317)
+                    return
+                if exc_context is None or exc_context is frame_exc:
+                    break
+                new_exc = exc_context
+            # Change the end of the chain to point to the exception
+            # we expect it to reference
+            new_exc.__context__ = old_exc
+        return _fix_exception_context
+
+    def _reraise_with_existing_context(exc_details):
+        try:
+            # bare "raise exc_details[1]" replaces our carefully
+            # set-up context
+            fixed_ctx = exc_details[1].__context__
+            raise exc_details[1]
+        except BaseException:
+            exc_details[1].__context__ = fixed_ctx
+            raise
+else:
+    # No exception context in Python 2
+    def _make_context_fixer(frame_exc):
+        return lambda new_exc, old_exc: None
+
+    # Use 3 argument raise in Python 2,
+    # but use exec to avoid SyntaxError in Python 3
+    def _reraise_with_existing_context(exc_details):
+        exc_type, exc_value, exc_tb = exc_details
+        exec ("raise exc_type, exc_value, exc_tb")
+
 # Inspired by discussions on http://bugs.python.org/issue13585
 class ExitStack(object):
     """Context manager for dynamic management of a stack of exit callbacks
@@ -152,7 +298,7 @@ class ExitStack(object):
             files = [stack.enter_context(open(fname)) for fname in filenames]
             # All opened files will automatically be closed at the end of
             # the with statement, even if attempts to open files later
-            # in the list throw an exception
+            # in the list raise an exception
 
     """
     def __init__(self):
@@ -177,8 +323,8 @@ class ExitStack(object):
 
         Can suppress exceptions the same way __exit__ methods can.
 
-        Also accepts any object with an __exit__ method (registering the
+        Also accepts any object with an __exit__ method (registering a call
-        method instead of the object itself)
+        to the method instead of the object itself)
         """
         # We use an unbound method rather than a bound method to follow
         # the standard lookup behaviour for special methods
@@ -226,40 +372,43 @@ class ExitStack(object):
         return self
 
     def __exit__(self, *exc_details):
-        if not self._exit_callbacks:
+        received_exc = exc_details[0] is not None
-            return
+
-        # This looks complicated, but it is really just
+        # We manipulate the exception state so it behaves as though
-        # setting up a chain of try-expect statements to ensure
+        # we were actually nesting multiple with statements
-        # that outer callbacks still get invoked even if an
+        frame_exc = sys.exc_info()[1]
-        # inner one throws an exception
+        _fix_exception_context = _make_context_fixer(frame_exc)
-        def _invoke_next_callback(exc_details):
+
-            # Callbacks are removed from the list in FIFO order
+        # Callbacks are invoked in LIFO order to match the behaviour of
-            # but the recursion means they're invoked in LIFO order
+        # nested context managers
-            cb = self._exit_callbacks.popleft()
+        suppressed_exc = False
-            if not self._exit_callbacks:
+        pending_raise = False
-                # Innermost callback is invoked directly
+        while self._exit_callbacks:
-                return cb(*exc_details)
+            cb = self._exit_callbacks.pop()
-            # More callbacks left, so descend another level in the stack
             try:
-                suppress_exc = _invoke_next_callback(exc_details)
+                if cb(*exc_details):
-            except:
+                    suppressed_exc = True
-                suppress_exc = cb(*sys.exc_info())
+                    pending_raise = False
-                # Check if this cb suppressed the inner exception
-                if not suppress_exc:
-                    raise
-            else:
-                # Check if inner cb suppressed the original exception
-                if suppress_exc:
                     exc_details = (None, None, None)
-                suppress_exc = cb(*exc_details) or suppress_exc
+            except:
-            return suppress_exc
+                new_exc_details = sys.exc_info()
-        # Kick off the recursive chain
+                # simulate the stack of exceptions by setting the context
-        return _invoke_next_callback(exc_details)
+                _fix_exception_context(new_exc_details[1], exc_details[1])
+                pending_raise = True
+                exc_details = new_exc_details
+        if pending_raise:
+            _reraise_with_existing_context(exc_details)
+        return received_exc and suppressed_exc
 
 # Preserve backwards compatibility
 class ContextStack(ExitStack):
     """Backwards compatibility alias for ExitStack"""
 
+    def __init__(self):
+        warnings.warn("ContextStack has been renamed to ExitStack",
+                      DeprecationWarning)
+        super(ContextStack, self).__init__()
+
     def register_exit(self, callback):
         return self.push(callback)
 

docs/index.rst

@@ -21,22 +21,25 @@ involving the ``with`` statement.
 Additions Relative to the Standard Library
 ------------------------------------------
 
-This module is primarily a backport of the Python 3.2 version of
+This module is primarily a backport of the Python 3.5 version of
 :mod:`contextlib` to earlier releases. However, it is also a proving ground
-for new features not yet part of the standard library. Those new features
+for new features not yet part of the standard library.
-are currently:
 
-* :class:`ExitStack`
+There are currently no such features in the module.
-* :meth:`ContextDecorator.refresh_cm`
+
+Refer to the :mod:`contextlib` documentation for details of which
+versions of Python 3 introduce the various APIs provided in this module.
 
 
 API Reference
 =============
 
-.. function:: contextmanager
+Functions and classes provided:
 
-   This function is a decorator that can be used to define a factory
+.. decorator:: contextmanager
-   function for ``with`` statement context managers, without needing to
+
+   This function is a :term:`decorator` that can be used to define a factory
+   function for :keyword:`with` statement context managers, without needing to
    create a class or separate :meth:`__enter__` and :meth:`__exit__` methods.
 
    A simple example (this is not recommended as a real way of generating HTML!)::
@@ -56,24 +59,24 @@ API Reference
       foo
       </h1>
 
-   The function being decorated must return a generator-iterator when
+   The function being decorated must return a :term:`generator`-iterator when
    called. This iterator must yield exactly one value, which will be bound to
-   the targets in the ``with`` statement's ``as`` clause, if any.
+   the targets in the :keyword:`with` statement's :keyword:`as` clause, if any.
 
-   At the point where the generator yields, the block nested in the ``with``
+   At the point where the generator yields, the block nested in the :keyword:`with`
    statement is executed.  The generator is then resumed after the block is exited.
    If an unhandled exception occurs in the block, it is reraised inside the
    generator at the point where the yield occurred.  Thus, you can use a
-   ``try``...\ ``except``...\ ``finally`` statement to trap
+   :keyword:`try`...\ :keyword:`except`...\ :keyword:`finally` statement to trap
    the error (if any), or ensure that some cleanup takes place. If an exception is
    trapped merely in order to log it or to perform some action (rather than to
    suppress it entirely), the generator must reraise that exception. Otherwise the
-   generator context manager will indicate to the ``with`` statement that
+   generator context manager will indicate to the :keyword:`with` statement that
    the exception has been handled, and execution will resume with the statement
-   immediately following the ``with`` statement.
+   immediately following the :keyword:`with` statement.
 
    :func:`contextmanager` uses :class:`ContextDecorator` so the context managers
-   it creates can be used as decorators as well as in ``with`` statements.
+   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
@@ -104,7 +107,97 @@ API Reference
               print(line)
 
    without needing to explicitly close ``page``.  Even if an error occurs,
-   ``page.close()`` will be called when the ``with`` block is exited.
+   ``page.close()`` will be called when the :keyword:`with` block is exited.
+
+
+.. function:: suppress(*exceptions)
+
+   Return a context manager that suppresses any of the specified exceptions
+   if they occur in the body of a with statement and then resumes execution
+   with the first statement following the end of the with statement.
+
+   As with any other mechanism that completely suppresses exceptions, this
+   context manager should be used only to cover very specific errors where
+   silently continuing with program execution is known to be the right
+   thing to do.
+
+   For example::
+
+       from contextlib import suppress
+
+       with suppress(FileNotFoundError):
+           os.remove('somefile.tmp')
+
+       with suppress(FileNotFoundError):
+           os.remove('someotherfile.tmp')
+
+   This code is equivalent to::
+
+       try:
+           os.remove('somefile.tmp')
+       except FileNotFoundError:
+           pass
+
+       try:
+           os.remove('someotherfile.tmp')
+       except FileNotFoundError:
+           pass
+
+   This context manager is :ref:`reentrant <reentrant-cms>`.
+
+   .. versionadded:: 0.5
+      Part of the standard library in Python 3.4 and later
+
+
+.. function:: redirect_stdout(new_target)
+
+   Context manager for temporarily redirecting :data:`sys.stdout` to
+   another file or file-like object.
+
+   This tool adds flexibility to existing functions or classes whose output
+   is hardwired to stdout.
+
+   For example, the output of :func:`help` normally is sent to *sys.stdout*.
+   You can capture that output in a string by redirecting the output to a
+   :class:`io.StringIO` object::
+
+        f = io.StringIO()
+        with redirect_stdout(f):
+            help(pow)
+        s = f.getvalue()
+
+   To send the output of :func:`help` to a file on disk, redirect the output
+   to a regular file::
+
+        with open('help.txt', 'w') as f:
+            with redirect_stdout(f):
+                help(pow)
+
+   To send the output of :func:`help` to *sys.stderr*::
+
+        with redirect_stdout(sys.stderr):
+            help(pow)
+
+   Note that the global side effect on :data:`sys.stdout` means that this
+   context manager is not suitable for use in library code and most threaded
+   applications. It also has no effect on the output of subprocesses.
+   However, it is still a useful approach for many utility scripts.
+
+   This context manager is :ref:`reentrant <reentrant-cms>`.
+
+   .. versionadded:: 0.5
+      Part of the standard library in Python 3.4 and later
+
+
+.. function:: redirect_stderr(new_target)
+
+   Similar to :func:`redirect_stdout`, but redirecting :data:`sys.stderr` to
+   another file or file-like object.
+
+   This context manager is :ref:`reentrant <reentrant-cms>`.
+
+   .. versionadded:: 0.5
+      Part of the standard library in Python 3.5 and later
 
 
 .. class:: ContextDecorator()
@@ -112,7 +205,7 @@ API Reference
    A base class that enables a context manager to also be used as a decorator.
 
    Context managers inheriting from ``ContextDecorator`` have to implement
-   :meth:`__enter__` and :meth:`__exit__` as normal. :meth:`__exit__` retains its optional
+   ``__enter__`` and ``__exit__`` as normal. ``__exit__`` retains its optional
    exception handling even when used as a decorator.
 
    ``ContextDecorator`` is used by :func:`contextmanager`, so you get this
@@ -174,22 +267,11 @@ API Reference
           def __exit__(self, *exc):
               return False
 
-   .. method:: refresh_cm()
+   .. note::
-
-      This method is invoked each time a call is made to a decorated function.
-      The default implementation just returns *self*.
-
       As the decorated function must be able to be called multiple times, the
-      underlying context manager must normally support use in multiple
+      underlying context manager must support use in multiple :keyword:`with`
-      ``with`` statements (preferably in a thread-safe manner). If
+      statements. If this is not the case, then the original construct with the
-      this is not the case, then the context manager must define this method
+      explicit :keyword:`with` statement inside the function should be used.
-      and return a *new* copy of the context manager on each invocation.
-
-      This may involve keeping a copy of the original arguments used to
-      first initialise the context manager.
-
-   .. versionchanged:: 0.1
-      Made the standard library's private :meth:`refresh_cm` API public
 
 
 .. class:: ExitStack()
@@ -205,20 +287,32 @@ API Reference
           files = [stack.enter_context(open(fname)) for fname in filenames]
           # All opened files will automatically be closed at the end of
           # the with statement, even if attempts to open files later
-          # in the list throw an exception
+          # in the list raise an exception
 
    Each instance maintains a stack of registered callbacks that are called in
    reverse order when the instance is closed (either explicitly or implicitly
-   at the end of a ``with`` statement). Note that callbacks are *not* invoked
+   at the end of a :keyword:`with` statement). Note that callbacks are *not*
-   implicitly when the context stack instance is garbage collected.
+   invoked implicitly when the context stack instance is garbage collected.
+
+   This stack model is used so that context managers that acquire their
+   resources in their ``__init__`` method (such as file objects) can be
+   handled correctly.
 
    Since registered callbacks are invoked in the reverse order of
-   registration, this ends up behaving as if multiple nested ``with``
+   registration, this ends up behaving as if multiple nested :keyword:`with`
    statements had been used with the registered set of callbacks. This even
    extends to exception handling - if an inner callback suppresses or replaces
    an exception, then outer callbacks will be passed arguments based on that
    updated state.
 
+   This is a relatively low level API that takes care of the details of
+   correctly unwinding the stack of exit callbacks. It provides a suitable
+   foundation for higher level context managers that manipulate the exit
+   stack in application specific ways.
+
+   .. versionadded:: 0.4
+      Part of the standard library in Python 3.3 and later
+
    .. method:: enter_context(cm)
 
       Enters a new context manager and adds its :meth:`__exit__` method to
@@ -226,21 +320,25 @@ API Reference
       manager's own :meth:`__enter__` method.
 
       These context managers may suppress exceptions just as they normally
-      would if used directly as part of a ``with`` statement.
+      would if used directly as part of a :keyword:`with` statement.
 
    .. method:: push(exit)
 
-      Directly accepts a callback with the same signature as a
+      Adds a context manager's :meth:`__exit__` method to the callback stack.
-      context manager's :meth:`__exit__` method and adds it to the callback
+
-      stack.
+      As ``__enter__`` is *not* invoked, this method can be used to cover
+      part of an :meth:`__enter__` implementation with a context manager's own
+      :meth:`__exit__` method.
+
+      If passed an object that is not a context manager, this method assumes
+      it is a callback with the same signature as a context manager's
+      :meth:`__exit__` method and adds it directly to the callback stack.
 
       By returning true values, these callbacks can suppress exceptions the
       same way context manager :meth:`__exit__` methods can.
 
-      This method also accepts any object with an ``__exit__`` method, and
+      The passed in object is returned from the function, allowing this
-      will register that method as the callback. This is mainly useful to
+      method to be used as a function decorator.
-      cover part of an :meth:`__enter__` implementation with a context
-      manager's own :meth:`__exit__` method.
 
    .. method:: callback(callback, *args, **kwds)
 
@@ -250,22 +348,27 @@ API Reference
       Unlike the other methods, callbacks added this way cannot suppress
       exceptions (as they are never passed the exception details).
 
+      The passed in callback is returned from the function, allowing this
+      method to be used as a function decorator.
+
    .. method:: pop_all()
 
-      Transfers the callback stack to a fresh instance and returns it. No
+      Transfers the callback stack to a fresh :class:`ExitStack` instance
-      callbacks are invoked by this operation - instead, they will now be
+      and returns it. No callbacks are invoked by this operation - instead,
-      invoked when the new stack is closed (either explicitly or implicitly).
+      they will now be invoked when the new stack is closed (either
+      explicitly or implicitly at the end of a :keyword:`with` statement).
 
       For example, a group of files can be opened as an "all or nothing"
       operation as follows::
 
          with ExitStack() as stack:
              files = [stack.enter_context(open(fname)) for fname in filenames]
+             # Hold onto the close method, but don't call it yet.
              close_files = stack.pop_all().close
              # If opening any file fails, all previously opened files will be
              # closed automatically. If all files are opened successfully,
              # they will remain open even after the with statement ends.
-             # close_files() can then be invoked explicitly to close them all
+             # close_files() can then be invoked explicitly to close them all.
 
    .. method:: close()
 
@@ -274,21 +377,6 @@ API Reference
       callbacks registered, the arguments passed in will indicate that no
       exception occurred.
 
-   .. versionadded:: 0.4
-      New API for :mod:`contextlib2`, not available in standard library
-
-
-.. class:: ContextStack()
-
-   An earlier incarnation of the :class:`ExitStack` interface. This class
-   is deprecated and should no longer be used.
-
-   .. versionchanged:: 0.4
-      Deprecated in favour of :class:`ExitStack`
-
-   .. versionadded:: 0.2
-      New API for :mod:`contextlib2`, not available in standard library
-
 
 Examples and Recipes
 ====================
@@ -299,53 +387,6 @@ the tools provided by :mod:`contextlib2`. Some of them may also work with
 case, it is noted at the end of the example.
 
 
-Using a context manager as a function decorator
------------------------------------------------
-
-:class:`ContextDecorator` makes it possible to use a context manager in
-both an ordinary ``with`` statement and also as a function decorator. The
-:meth:`ContextDecorator.refresh_cm` method even makes it possible to use
-otherwise single use context managers (such as those created by
-:func:`contextmanager`) that way.
-
-For example, it is sometimes useful to wrap functions or groups of statements
-with a logger that can track the time of entry and time of exit.  Rather than
-writing both a function decorator and a context manager for the task,
-:func:`contextmanager` provides both capabilities in a single
-definition::
-
-    from contextlib2 import contextmanager
-    import logging
-
-    logging.basicConfig(level=logging.INFO)
-
-    @contextmanager
-    def track_entry_and_exit(name):
-        logging.info('Entering: {}'.format(name))
-        yield
-        logging.info('Exiting: {}'.format(name))
-
-This can be used as both a context manager::
-
-    with track_entry_and_exit('widget loader'):
-        print('Some time consuming activity goes here')
-        load_widget()
-
-And also as a function decorator::
-
-    @track_entry_and_exit('widget loader')
-    def activity():
-        print('Some time consuming activity goes here')
-        load_widget()
-
-Note that there is one additional limitation when using context managers
-as function decorators: there's no way to access the return value of
-:meth:`__enter__`. If that value is needed, then it is still necessary to use
-an explicit ``with`` statement.
-
-This example should also work with :mod:`contextlib` in Python 3.2.1 or later.
-
-
 Cleaning up in an ``__enter__`` implementation
 ----------------------------------------------
 
@@ -384,6 +425,8 @@ and maps them to the context management protocol::
            # We don't need to duplicate any of our resource release logic
            self.release_resource()
 
+This example will also work with :mod:`contextlib` in Python 3.3 or later.
+
 
 Replacing any use of ``try-finally`` and flag variables
 -------------------------------------------------------
@@ -456,7 +499,174 @@ advance::
 
 Due to the way the decorator protocol works, a callback function
 declared this way cannot take any parameters. Instead, any resources to
-be released must be accessed as closure variables
+be released must be accessed as closure variables.
+
+This example will also work with :mod:`contextlib` in Python 3.3 or later.
+
+
+Using a context manager as a function decorator
+-----------------------------------------------
+
+:class:`ContextDecorator` makes it possible to use a context manager in
+both an ordinary ``with`` statement and also as a function decorator. The
+:meth:`ContextDecorator.refresh_cm` method even makes it possible to use
+otherwise single use context managers (such as those created by
+:func:`contextmanager`) that way.
+
+For example, it is sometimes useful to wrap functions or groups of statements
+with a logger that can track the time of entry and time of exit.  Rather than
+writing both a function decorator and a context manager for the task,
+:func:`contextmanager` provides both capabilities in a single
+definition::
+
+    from contextlib2 import contextmanager
+    import logging
+
+    logging.basicConfig(level=logging.INFO)
+
+    @contextmanager
+    def track_entry_and_exit(name):
+        logging.info('Entering: {}'.format(name))
+        yield
+        logging.info('Exiting: {}'.format(name))
+
+This can be used as both a context manager::
+
+    with track_entry_and_exit('widget loader'):
+        print('Some time consuming activity goes here')
+        load_widget()
+
+And also as a function decorator::
+
+    @track_entry_and_exit('widget loader')
+    def activity():
+        print('Some time consuming activity goes here')
+        load_widget()
+
+Note that there is one additional limitation when using context managers
+as function decorators: there's no way to access the return value of
+:meth:`__enter__`. If that value is needed, then it is still necessary to use
+an explicit ``with`` statement.
+
+This example will also work with :mod:`contextlib` in Python 3.2.1 or later.
+
+
+Context Management Concepts
+===========================
+
+.. _single-use-reusable-and-reentrant-cms:
+
+Single use, reusable and reentrant context managers
+---------------------------------------------------
+
+Most context managers are written in a way that means they can only be
+used effectively in a :keyword:`with` statement once. These single use
+context managers must be created afresh each time they're used -
+attempting to use them a second time will trigger an exception or
+otherwise not work correctly.
+
+This common limitation means that it is generally advisable to create
+context managers directly in the header of the :keyword:`with` statement
+where they are used (as shown in all of the usage examples above).
+
+Files are an example of effectively single use context managers, since
+the first :keyword:`with` statement will close the file, preventing any
+further IO operations using that file object.
+
+Context managers created using :func:`contextmanager` are also single use
+context managers, and will complain about the underlying generator failing
+to yield if an attempt is made to use them a second time::
+
+    >>> from contextlib import contextmanager
+    >>> @contextmanager
+    ... def singleuse():
+    ...     print("Before")
+    ...     yield
+    ...     print("After")
+    ...
+    >>> cm = singleuse()
+    >>> with cm:
+    ...     pass
+    ...
+    Before
+    After
+    >>> with cm:
+    ...    pass
+    ...
+    Traceback (most recent call last):
+        ...
+    RuntimeError: generator didn't yield
+
+
+.. _reentrant-cms:
+
+Reentrant context managers
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+More sophisticated context managers may be "reentrant". These context
+managers can not only be used in multiple :keyword:`with` statements,
+but may also be used *inside* a :keyword:`with` statement that is already
+using the same context manager.
+
+:class:`threading.RLock` is an example of a reentrant context manager, as is
+:func:`suppress`. Here's a toy example of reentrant use (real world
+examples of reentrancy are more likely to occur with objects like recursive
+locks and are likely to be far more complicated than this example)::
+
+    >>> from contextlib import suppress
+    >>> ignore_raised_exception = suppress(ZeroDivisionError)
+    >>> with ignore_raised_exception:
+    ...     with ignore_raised_exception:
+    ...         1/0
+    ...     print("This line runs")
+    ...     1/0
+    ...     print("This is skipped")
+    ...
+    This line runs
+    >>> # The second exception is also suppressed
+
+
+.. _reusable-cms:
+
+Reusable context managers
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Distinct from both single use and reentrant context managers are "reusable"
+context managers (or, to be completely explicit, "reusable, but not
+reentrant" context managers, since reentrant context managers are also
+reusable). These context managers support being used multiple times, but
+will fail (or otherwise not work correctly) if the specific context manager
+instance has already been used in a containing with statement.
+
+An example of a reusable context manager is :func:`redirect_stdout`::
+
+    >>> from contextlib import redirect_stdout
+    >>> from io import StringIO
+    >>> f = StringIO()
+    >>> collect_output = redirect_stdout(f)
+    >>> with collect_output:
+    ...     print("Collected")
+    ...
+    >>> print("Not collected")
+    Not collected
+    >>> with collect_output:
+    ...     print("Also collected")
+    ...
+    >>> print(f.getvalue())
+    Collected
+    Also collected
+
+However, this context manager is not reentrant, so attempting to reuse it
+within a containing with statement fails:
+
+    >>> with collect_output:
+    ...     # Nested reuse is not permitted
+    ...     with collect_output:
+    ...         pass
+    ...
+    Traceback (most recent call last):
+      ...
+    RuntimeError: Cannot reenter <...>
 
 
 Obtaining the Module

setup.py

@@ -1,9 +1,9 @@
 #!/usr/bin/env python
 from distutils.core import setup
 
-# Technically, unittest2 is a dependency to run the tests on 2.6 and 3.1
+# Technically, unittest2 is a dependency to run the tests on 2.7
-# This file ignores that, since I don't want to depend on distribute
+# This file ignores that, since I don't want to depend on
-# or setuptools just to get "tests_require" support
+# setuptools just to get "tests_require" support
 
 setup(
     name='contextlib2',
@@ -14,5 +14,16 @@ setup(
     long_description=open('README.md').read(),
     author='Nick Coghlan',
     author_email='ncoghlan@gmail.com',
-    url='http://contextlib2.readthedocs.org'
+    url='http://contextlib2.readthedocs.org',
+    classifiers=[
+        'Development Status :: 5 - Production/Stable',
+        'License :: OSI Approved :: Python Software Foundation License',
+        # These are the Python versions tested, it may work on others
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.5',
+    ],
+
 )

test_contextlib2.py

@@ -1,14 +1,19 @@
-#!/usr/bin/env python
+"""Unit tests for contextlib2.py"""
-"""Unit tests for contextlib2"""
+from __future__ import print_function
+from __future__ import unicode_literals
 
+import io
 import sys
-
 import unittest
-if not hasattr(unittest, "skipIf"):
+import __future__ # For PEP 479 conditional test
-    import unittest2 as unittest
+import contextlib2
-
 from contextlib2 import *  # Tests __all__
 
+if not hasattr(unittest.TestCase, "assertRaisesRegex"):
+    import unittest2 as unittest
+
+requires_docstrings = unittest.skipIf(sys.flags.optimize >= 2,
+                                      "Test requires docstrings")
 
 class ContextManagerTestCase(unittest.TestCase):
 
@@ -81,6 +86,44 @@ class ContextManagerTestCase(unittest.TestCase):
             raise ZeroDivisionError(999)
         self.assertEqual(state, [1, 42, 999])
 
+    def test_contextmanager_except_stopiter(self):
+        stop_exc = StopIteration('spam')
+        @contextmanager
+        def woohoo():
+            yield
+        try:
+            with self.assertWarnsRegex(PendingDeprecationWarning,
+                                       "StopIteration"):
+                with woohoo():
+                    raise stop_exc
+        except Exception as ex:
+            self.assertIs(ex, stop_exc)
+        else:
+            self.fail('StopIteration was suppressed')
+
+    @unittest.skipUnless(hasattr(__future__, "generator_stop"),
+                         "Test only valid for versions implementing PEP 479")
+    def test_contextmanager_except_pep479(self):
+        code = """\
+from __future__ import generator_stop
+from contextlib import contextmanager
+@contextmanager
+def woohoo():
+    yield
+"""
+        locals = {}
+        exec(code, locals, locals)
+        woohoo = locals['woohoo']
+
+        stop_exc = StopIteration('spam')
+        try:
+            with woohoo():
+                raise stop_exc
+        except Exception as ex:
+            self.assertIs(ex, stop_exc)
+        else:
+            self.fail('StopIteration was suppressed')
+
     def _create_contextmanager_attribs(self):
         def attribs(**kw):
             def decorate(func):
@@ -99,15 +142,33 @@ class ContextManagerTestCase(unittest.TestCase):
         self.assertEqual(baz.__name__,'baz')
         self.assertEqual(baz.foo, 'bar')
 
-    @unittest.skipIf(sys.flags.optimize >= 2,
+    @requires_docstrings
-                     "Docstrings are omitted with -O2 and above")
     def test_contextmanager_doc_attrib(self):
         baz = self._create_contextmanager_attribs()
         self.assertEqual(baz.__doc__, "Whee!")
 
+    @requires_docstrings
+    def test_instance_docstring_given_cm_docstring(self):
+        baz = self._create_contextmanager_attribs()(None)
+        self.assertEqual(baz.__doc__, "Whee!")
+
+    def test_keywords(self):
+        # Ensure no keyword arguments are inhibited
+        @contextmanager
+        def woohoo(self, func, args, kwds):
+            yield (self, func, args, kwds)
+        with woohoo(self=11, func=22, args=33, kwds=44) as target:
+            self.assertEqual(target, (11, 22, 33, 44))
+
+
 class ClosingTestCase(unittest.TestCase):
 
-    # XXX This needs more work
+    @requires_docstrings
+    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 = []
@@ -135,6 +196,7 @@ class ClosingTestCase(unittest.TestCase):
 
 
 class mycontext(ContextDecorator):
+    """Example decoration-compatible context manager for testing"""
     started = False
     exc = None
     catch = False
@@ -150,6 +212,13 @@ class mycontext(ContextDecorator):
 
 class TestContextDecorator(unittest.TestCase):
 
+    @requires_docstrings
+    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:
@@ -162,12 +231,11 @@ class TestContextDecorator(unittest.TestCase):
     def test_contextdecorator_with_exception(self):
         context = mycontext()
 
-        with self.assertRaises(NameError):
+        with self.assertRaisesRegex(NameError, 'foo'):
             with context:
                 raise NameError('foo')
         self.assertIsNotNone(context.exc)
         self.assertIs(context.exc[0], NameError)
-        self.assertIn('foo', str(context.exc[1]))
 
         context = mycontext()
         context.catch = True
@@ -197,11 +265,10 @@ class TestContextDecorator(unittest.TestCase):
             self.assertTrue(context.started)
             raise NameError('foo')
 
-        with self.assertRaises(NameError):
+        with self.assertRaisesRegex(NameError, 'foo'):
             test()
         self.assertIsNotNone(context.exc)
         self.assertIs(context.exc[0], NameError)
-        self.assertIn('foo', str(context.exc[1]))
 
 
     def test_decorating_method(self):
@@ -302,9 +369,18 @@ class TestContextDecorator(unittest.TestCase):
         test('something else')
         self.assertEqual(state, [1, 'something else', 999])
 
+# Detailed exception chaining checks only make sense on Python 3
+check_exception_chaining = contextlib2._HAVE_EXCEPTION_CHAINING
 
 class TestExitStack(unittest.TestCase):
 
+    @requires_docstrings
+    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
@@ -416,6 +492,211 @@ class TestExitStack(unittest.TestCase):
         new_stack.close()
         self.assertEqual(result, [1, 2, 3])
 
+    def test_exit_raise(self):
+        with self.assertRaises(ZeroDivisionError):
+            with ExitStack() as stack:
+                stack.push(lambda *exc: False)
+                1/0
+
+    def test_exit_suppress(self):
+        with ExitStack() as stack:
+            stack.push(lambda *exc: True)
+            1/0
+
+    def test_exit_exception_chaining_reference(self):
+        # Sanity check to make sure that ExitStack chaining matches
+        # actual nested with statements
+        class RaiseExc:
+            def __init__(self, exc):
+                self.exc = exc
+            def __enter__(self):
+                return self
+            def __exit__(self, *exc_details):
+                raise self.exc
+
+        class RaiseExcWithContext:
+            def __init__(self, outer, inner):
+                self.outer = outer
+                self.inner = inner
+            def __enter__(self):
+                return self
+            def __exit__(self, *exc_details):
+                try:
+                    raise self.inner
+                except:
+                    raise self.outer
+
+        class SuppressExc:
+            def __enter__(self):
+                return self
+            def __exit__(self, *exc_details):
+                self.__class__.saved_details = exc_details
+                return True
+
+        try:
+            with RaiseExc(IndexError):
+                with RaiseExcWithContext(KeyError, AttributeError):
+                    with SuppressExc():
+                        with RaiseExc(ValueError):
+                            1 / 0
+        except IndexError as exc:
+            if check_exception_chaining:
+                self.assertIsInstance(exc.__context__, KeyError)
+                self.assertIsInstance(exc.__context__.__context__, AttributeError)
+                # Inner exceptions were suppressed
+                self.assertIsNone(exc.__context__.__context__.__context__)
+        else:
+            self.fail("Expected IndexError, but no exception was raised")
+        # Check the inner exceptions
+        inner_exc = SuppressExc.saved_details[1]
+        self.assertIsInstance(inner_exc, ValueError)
+        if check_exception_chaining:
+            self.assertIsInstance(inner_exc.__context__, ZeroDivisionError)
+
+    def test_exit_exception_chaining(self):
+        # Ensure exception chaining matches the reference behaviour
+        def raise_exc(exc):
+            raise exc
+
+        saved_details = [None]
+        def suppress_exc(*exc_details):
+            saved_details[0] = exc_details
+            return True
+
+        try:
+            with ExitStack() as stack:
+                stack.callback(raise_exc, IndexError)
+                stack.callback(raise_exc, KeyError)
+                stack.callback(raise_exc, AttributeError)
+                stack.push(suppress_exc)
+                stack.callback(raise_exc, ValueError)
+                1 / 0
+        except IndexError as exc:
+            if check_exception_chaining:
+                self.assertIsInstance(exc.__context__, KeyError)
+                self.assertIsInstance(exc.__context__.__context__, AttributeError)
+                # Inner exceptions were suppressed
+                self.assertIsNone(exc.__context__.__context__.__context__)
+        else:
+            self.fail("Expected IndexError, but no exception was raised")
+        # Check the inner exceptions
+        inner_exc = saved_details[0][1]
+        self.assertIsInstance(inner_exc, ValueError)
+        if check_exception_chaining:
+            self.assertIsInstance(inner_exc.__context__, ZeroDivisionError)
+
+    def test_exit_exception_non_suppressing(self):
+        # http://bugs.python.org/issue19092
+        def raise_exc(exc):
+            raise exc
+
+        def suppress_exc(*exc_details):
+            return True
+
+        try:
+            with ExitStack() as stack:
+                stack.callback(lambda: None)
+                stack.callback(raise_exc, IndexError)
+        except Exception as exc:
+            self.assertIsInstance(exc, IndexError)
+        else:
+            self.fail("Expected IndexError, but no exception was raised")
+
+        try:
+            with ExitStack() as stack:
+                stack.callback(raise_exc, KeyError)
+                stack.push(suppress_exc)
+                stack.callback(raise_exc, IndexError)
+        except Exception as exc:
+            self.assertIsInstance(exc, KeyError)
+        else:
+            self.fail("Expected KeyError, but no exception was raised")
+
+    def test_exit_exception_with_correct_context(self):
+        # http://bugs.python.org/issue20317
+        @contextmanager
+        def gets_the_context_right(exc):
+            try:
+                yield
+            finally:
+                raise exc
+
+        exc1 = Exception(1)
+        exc2 = Exception(2)
+        exc3 = Exception(3)
+        exc4 = Exception(4)
+
+        # The contextmanager already fixes the context, so prior to the
+        # fix, ExitStack would try to fix it *again* and get into an
+        # infinite self-referential loop
+        try:
+            with ExitStack() as stack:
+                stack.enter_context(gets_the_context_right(exc4))
+                stack.enter_context(gets_the_context_right(exc3))
+                stack.enter_context(gets_the_context_right(exc2))
+                raise exc1
+        except Exception as exc:
+            self.assertIs(exc, exc4)
+            if check_exception_chaining:
+                self.assertIs(exc.__context__, exc3)
+                self.assertIs(exc.__context__.__context__, exc2)
+                self.assertIs(exc.__context__.__context__.__context__, exc1)
+                self.assertIsNone(
+                        exc.__context__.__context__.__context__.__context__)
+
+    def test_exit_exception_with_existing_context(self):
+        # Addresses a lack of test coverage discovered after checking in a
+        # fix for issue 20317 that still contained debugging code.
+        def raise_nested(inner_exc, outer_exc):
+            try:
+                raise inner_exc
+            finally:
+                raise outer_exc
+        exc1 = Exception(1)
+        exc2 = Exception(2)
+        exc3 = Exception(3)
+        exc4 = Exception(4)
+        exc5 = Exception(5)
+        try:
+            with ExitStack() as stack:
+                stack.callback(raise_nested, exc4, exc5)
+                stack.callback(raise_nested, exc2, exc3)
+                raise exc1
+        except Exception as exc:
+            self.assertIs(exc, exc5)
+            if check_exception_chaining:
+                self.assertIs(exc.__context__, exc4)
+                self.assertIs(exc.__context__.__context__, exc3)
+                self.assertIs(exc.__context__.__context__.__context__, exc2)
+                self.assertIs(
+                    exc.__context__.__context__.__context__.__context__, exc1)
+                self.assertIsNone(
+                    exc.__context__.__context__.__context__.__context__.__context__)
+
+
+
+    def test_body_exception_suppress(self):
+        def suppress_exc(*exc_details):
+            return True
+        try:
+            with ExitStack() as stack:
+                stack.push(suppress_exc)
+                1/0
+        except IndexError as exc:
+            self.fail("Expected no exception, got IndexError")
+
+    def test_exit_exception_chaining_suppress(self):
+        with ExitStack() as stack:
+            stack.push(lambda *exc: True)
+            stack.push(lambda *exc: 1/0)
+            stack.push(lambda *exc: {}[1])
+
+    def test_excessive_nesting(self):
+        # The original implementation would die with RecursionError here
+        with ExitStack() as stack:
+            for i in range(10000):
+                stack.callback(int)
+
     def test_instance_bypass(self):
         class Example(object): pass
         cm = Example()
@@ -426,128 +707,129 @@ class TestExitStack(unittest.TestCase):
         self.assertIs(stack._exit_callbacks[-1], cm)
 
 
-class TestContextStack(unittest.TestCase):
+class TestRedirectStream:
 
-    def test_no_resources(self):
+    redirect_stream = None
-        with ContextStack():
+    orig_stream = None
-            pass
 
-    def test_register(self):
+    @requires_docstrings
-        expected = [
+    def test_instance_docs(self):
-            ((), {}),
+        # Issue 19330: ensure context manager instances have good docstrings
-            ((1,), {}),
+        cm_docstring = self.redirect_stream.__doc__
-            ((1,2), {}),
+        obj = self.redirect_stream(None)
-            ((), dict(example=1)),
+        self.assertEqual(obj.__doc__, cm_docstring)
-            ((1,), dict(example=1)),
-            ((1,2), dict(example=1)),
-        ]
-        result = []
-        def _exit(*args, **kwds):
-            """Test metadata propagation"""
-            result.append((args, kwds))
-        with ContextStack() as stack:
-            for args, kwds in reversed(expected):
-                if args and kwds:
-                    f = stack.register(_exit, *args, **kwds)
-                elif args:
-                    f = stack.register(_exit, *args)
-                elif kwds:
-                    f = stack.register(_exit, **kwds)
-                else:
-                    f = stack.register(_exit)
-                self.assertIs(f, _exit)
-            for wrapper in stack._exit_callbacks:
-                self.assertIs(wrapper.__wrapped__, _exit)
-                self.assertNotEqual(wrapper.__name__, _exit.__name__)
-                self.assertIsNone(wrapper.__doc__, _exit.__doc__)
-        self.assertEqual(result, expected)
 
-    def test_register_exit(self):
+    def test_no_redirect_in_init(self):
-        exc_raised = ZeroDivisionError
+        orig_stdout = getattr(sys, self.orig_stream)
-        def _expect_exc(exc_type, exc, exc_tb):
+        self.redirect_stream(None)
-            self.assertIs(exc_type, exc_raised)
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
-        def _suppress_exc(*exc_details):
+
-            return True
+    def test_redirect_to_string_io(self):
-        def _expect_ok(exc_type, exc, exc_tb):
+        f = io.StringIO()
-            self.assertIsNone(exc_type)
+        msg = "Consider an API like help(), which prints directly to stdout"
-            self.assertIsNone(exc)
+        orig_stdout = getattr(sys, self.orig_stream)
-            self.assertIsNone(exc_tb)
+        with self.redirect_stream(f):
-        class ExitCM(object):
+            print(msg, file=getattr(sys, self.orig_stream))
-            def __init__(self, check_exc):
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
-                self.check_exc = check_exc
+        s = f.getvalue().strip()
-            def __enter__(self):
+        self.assertEqual(s, msg)
-                self.fail("Should not be called!")
+
-            def __exit__(self, *exc_details):
+    def test_enter_result_is_target(self):
-                self.check_exc(*exc_details)
+        f = io.StringIO()
-        with ContextStack() as stack:
+        with self.redirect_stream(f) as enter_result:
-            stack.register_exit(_expect_ok)
+            self.assertIs(enter_result, f)
-            self.assertIs(stack._exit_callbacks[-1], _expect_ok)
+
-            cm = ExitCM(_expect_ok)
+    def test_cm_is_reusable(self):
-            stack.register_exit(cm)
+        f = io.StringIO()
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
+        write_to_f = self.redirect_stream(f)
-            stack.register_exit(_suppress_exc)
+        orig_stdout = getattr(sys, self.orig_stream)
-            self.assertIs(stack._exit_callbacks[-1], _suppress_exc)
+        with write_to_f:
-            cm = ExitCM(_expect_exc)
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
-            stack.register_exit(cm)
+        with write_to_f:
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
+            print("World!", file=getattr(sys, self.orig_stream))
-            stack.register_exit(_expect_exc)
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
-            self.assertIs(stack._exit_callbacks[-1], _expect_exc)
+        s = f.getvalue()
-            stack.register_exit(_expect_exc)
+        self.assertEqual(s, "Hello World!\n")
-            self.assertIs(stack._exit_callbacks[-1], _expect_exc)
+
+    def test_cm_is_reentrant(self):
+        f = io.StringIO()
+        write_to_f = self.redirect_stream(f)
+        orig_stdout = getattr(sys, self.orig_stream)
+        with write_to_f:
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
+            with write_to_f:
+                print("World!", file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+        s = f.getvalue()
+        self.assertEqual(s, "Hello World!\n")
+
+
+class TestRedirectStdout(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stdout
+    orig_stream = "stdout"
+
+
+class TestRedirectStderr(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stderr
+    orig_stream = "stderr"
+
+
+class TestSuppress(unittest.TestCase):
+
+    @requires_docstrings
+    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)
+
+    def test_no_exception(self):
+        with suppress(ValueError):
+            self.assertEqual(pow(2, 5), 32)
+
+    def test_exact_exception(self):
+        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_enter_context(self):
+    def test_cm_is_reentrant(self):
-        class TestCM(object):
+        ignore_exceptions = suppress(Exception)
-            def __enter__(self):
+        with ignore_exceptions:
-                result.append(1)
+            pass
-            def __exit__(self, *exc_details):
+        with ignore_exceptions:
-                result.append(3)
+            len(5)
-
+        with ignore_exceptions:
-        result = []
+            with ignore_exceptions: # Check nested usage
-        cm = TestCM()
+                len(5)
-        with ContextStack() as stack:
+            outer_continued = True
-            @stack.register  # Registered first => cleaned up last
+            1/0
-            def _exit():
+        self.assertTrue(outer_continued)
-                result.append(4)
-            self.assertIsNotNone(_exit)
-            stack.enter_context(cm)
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
-            result.append(2)
-        self.assertEqual(result, [1, 2, 3, 4])
-
-    def test_close(self):
-        result = []
-        with ContextStack() as stack:
-            @stack.register
-            def _exit():
-                result.append(1)
-            self.assertIsNotNone(_exit)
-            stack.close()
-            result.append(2)
-        self.assertEqual(result, [1, 2])
-
-    def test_preserve(self):
-        result = []
-        with ContextStack() as stack:
-            @stack.register
-            def _exit():
-                result.append(3)
-            self.assertIsNotNone(_exit)
-            new_stack = stack.preserve()
-            result.append(1)
-        result.append(2)
-        new_stack.close()
-        self.assertEqual(result, [1, 2, 3])
-
-    def test_instance_bypass(self):
-        class Example(object): pass
-        cm = Example()
-        cm.__exit__ = object()
-        stack = ContextStack()
-        self.assertRaises(AttributeError, stack.enter_context, cm)
-        stack.register_exit(cm)
-        self.assertIs(stack._exit_callbacks[-1], cm)
 
 if __name__ == "__main__":
     import unittest
-    unittest.main(__name__)
+    unittest.main()

tox.ini

@@ -4,3 +4,8 @@ envlist = py27, pypy, py34, py35, pypy3
 [testenv]
 commands = {envpython} test_contextlib2.py
 
+[testenv:py27]
+deps = unittest2
+
+[testenv:pypy]
+deps = unittest2