Merge with 3.2.
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index c0c75f7..4a7efe1 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -1047,6 +1047,15 @@
*start* and *end* are interpreted as in slice notation. Return ``-1`` if
*sub* is not found.
+ .. note::
+
+ The :meth:`~str.find` method should be used only if you need to know the
+ position of *sub*. To check if *sub* is a substring or not, use the
+ :keyword:`in` operator::
+
+ >>> 'Py' in 'Python'
+ True
+
.. method:: str.format(*args, **kwargs)