document default value for fillvalue

diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 5d3593e52cacb08c660c9efdf39c71b249bb7301..13d3147827b59745aa8c921e515346583d14907d 100644 (file)
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -368,9 +368,10 @@ loops that truncate the stream.
           except IndexError:
               pass
 
-   If one of the iterables is potentially infinite, then the :func:`izip_longest`
-   function should be wrapped with something that limits the number of calls (for
-   example :func:`islice` or :func:`takewhile`).
+   If one of the iterables is potentially infinite, then the
+   :func:`izip_longest` function should be wrapped with something that limits
+   the number of calls (for example :func:`islice` or :func:`takewhile`).  If
+   not specified, *fillvalue* defaults to ``None``.
 
    .. versionadded:: 2.6