Fix punctuation.
diff --git a/Doc/tutorial/classes.rst b/Doc/tutorial/classes.rst
index 1488329..db52f5e 100644
--- a/Doc/tutorial/classes.rst
+++ b/Doc/tutorial/classes.rst
@@ -537,7 +537,7 @@
=================
"Private" instance variables that cannot be accessed except from inside an
-object, don't exist in Python. However, there is a convention that is followed
+object don't exist in Python. However, there is a convention that is followed
by most Python code: a name prefixed with an underscore (e.g. ``_spam``) should
be treated as a non-public part of the API (whether it is a function, a method
or a data member). It should be considered an implementation detail and subject