Issue 9110. Adding ContextDecorator to contextlib. This enables the creation of APIs that act as decorators as well as context managers. contextlib.contextmanager changed to use ContextDecorator.

1 files changed, 57 insertions, 0 deletions

diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
index 2ee9e8d989..7a46834a13 100644
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -51,6 +51,11 @@ Functions provided:
    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.
+
+   .. versionchanged:: 3.2
+      Use of :class:`ContextDecorator`.
 
 .. function:: closing(thing)
 
@@ -79,6 +84,58 @@ Functions provided:
    ``page.close()`` will be called when the :keyword:`with` block is exited.
 
 
+.. class:: ContextDecorator()
+
+   A base class that enables a context manager to also be used as a decorator.
+
+   Context managers inheriting from ``ContextDecorator`` have to implement
+   ``__enter__`` and ``__exit__`` as normal. ``__exit__`` retains its optional
+   exception handling even when used as a decorator.
+
+   Example::
+
+      from contextlib import ContextDecorator
+
+      class mycontext(ContextDecorator):
+         def __enter__(self):
+            print('Starting')
+            return self
+
+         def __exit__(self, *exc):
+            print('Finishing')
+            return False
+
+      >>> @mycontext()
+      ... def function():
+      ...    print('The bit in the middle')
+      ...
+      >>> function()
+      Starting
+      The bit in the middle
+      Finishing
+
+      >>> with mycontext():
+      ...    print('The bit in the middle')
+      ...
+      Starting
+      The bit in the middle
+      Finishing
+
+   Existing context managers that already have a base class can be extended by
+   using ``ContextDecorator`` as a mixin class::
+
+      from contextlib import ContextDecorator
+
+      class mycontext(ContextBaseClass, ContextDecorator):
+         def __enter__(self):
+            return self
+
+         def __exit__(self, *exc):
+            return False
+
+   .. versionadded:: 3.2
+
+
 .. seealso::
 
    :pep:`0343` - The "with" statement