Replaced variable o with obj in operator.rst because o is easy to
confuse.
Added a note about Python 3's collections.Mapping etc., above section
that describes isMappingType() etc.
Added xrefs between os, os.path, fileinput, and open().
diff --git a/Doc/library/fileinput.rst b/Doc/library/fileinput.rst
index d45def1..b3f7e61 100644
--- a/Doc/library/fileinput.rst
+++ b/Doc/library/fileinput.rst
@@ -7,8 +7,9 @@
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
-This module implements a helper class and functions to quickly write a loop over
-standard input or a list of files.
+This module implements a helper class and functions to quickly write a
+loop over standard input or a list of files. If you just want to read or
+write one file see :func:`open`.
The typical use is::