Issue #12797: Added custom opener parameter to builtin open() and FileIO.open().
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index f63cea4..f9af3d8 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -776,7 +776,7 @@
:meth:`__index__` method that returns an integer.
-.. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True)
+.. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
Open *file* and return a corresponding stream. If the file cannot be opened,
an :exc:`OSError` is raised.
@@ -883,6 +883,15 @@
closed. If a filename is given *closefd* has no effect and must be ``True``
(the default).
+ A custom opener can be used by passing a callable as *opener*. The underlying
+ file descriptor for the file object is then obtained by calling *opener* with
+ (*file*, *flags*). *opener* must return an open file descriptor (passing
+ :mod:`os.open` as *opener* results in functionality similar to passing
+ ``None``).
+
+ .. versionchanged:: 3.3
+ The *opener* parameter was added.
+
The type of file object returned by the :func:`open` function depends on the
mode. When :func:`open` is used to open a file in a text mode (``'w'``,
``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a subclass of