Python Tutorial typo fix (#128077)

Author: shallow-beach

Doc/tutorial/classes.rst

@@ -325,7 +325,7 @@ Now what can we do with instance objects?  The only operations understood by
 instance objects are attribute references.  There are two kinds of valid
 attribute names: data attributes and methods.
 
-*data attributes* correspond to "instance variables" in Smalltalk, and to "data
+*Data attributes* correspond to "instance variables" in Smalltalk, and to "data
 members" in C++.  Data attributes need not be declared; like local variables,
 they spring into existence when they are first assigned to.  For example, if
 ``x`` is the instance of :class:`!MyClass` created above, the following piece of