Fix minor docs markup errors.
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
index 2d79a00..89589bc 100644
--- a/Doc/tutorial/datastructures.rst
+++ b/Doc/tutorial/datastructures.rst
@@ -179,9 +179,9 @@
``filter(function, sequence)`` returns a sequence consisting of those items from
the sequence for which ``function(item)`` is true. If *sequence* is a
-:class:`string` or :class:`tuple`, the result will be of the same type;
-otherwise, it is always a :class:`list`. For example, to compute a sequence of
-numbers divisible by 3 or 5::
+:class:`str`, :class:`unicode` or :class:`tuple`, the result will be of the
+same type; otherwise, it is always a :class:`list`. For example, to compute a
+sequence of numbers divisible by 3 or 5::
>>> def f(x): return x % 3 == 0 or x % 5 == 0
...