Expand file objects in datamodel to include methods

Author: cmaloney

Doc/reference/datamodel.rst

@@ -1385,12 +1385,28 @@ also :func:`os.popen`, :func:`os.fdopen`, and the
 :meth:`~socket.socket.makefile` method of socket objects (and perhaps by
 other functions or methods provided by extension modules).
 
+File objects implement common methods, listed below, to simplify usage in
+generic code. They are expected to be :ref:`context-managers`.
+
 The objects ``sys.stdin``, ``sys.stdout`` and ``sys.stderr`` are
 initialized to file objects corresponding to the interpreter's standard
 input, output and error streams; they are all open in text mode and
 therefore follow the interface defined by the :class:`io.TextIOBase`
 abstract class.
 
+.. method:: file.read(size=-1, /)
+
+   Retrieve up to *size* data from the file. As a convenience if *size* is
+   unspecified or -1 retrieve all data available.
+
+.. method:: file.write(data, /)
+
+   Store *data* to the file.
+
+.. method:: file.close()
+
+   Flush any buffers and close the underlying file.
+
 
 Internal types
 --------------