gh-106318: Add example for str.format() (GH-137018)

(cherry picked from commit 0cde70b)

Co-authored-by: Adorilson Bezerra <adorilson@gmail.com>

Author: adorilson

Doc/library/stdtypes.rst

@@ -1994,10 +1994,16 @@ expression support in the :mod:`re` module).
    ``{}``.  Each replacement field contains either the numeric index of a
    positional argument, or the name of a keyword argument.  Returns a copy of
    the string where each replacement field is replaced with the string value of
-   the corresponding argument.
+   the corresponding argument. For example:
+
+   .. doctest::
 
       >>> "The sum of 1 + 2 is {0}".format(1+2)
       'The sum of 1 + 2 is 3'
+      >>> "The sum of {a} + {b} is {answer}".format(answer=1+2, a=1, b=2)
+      'The sum of 1 + 2 is 3'
+      >>> "{1} expects the {0} Inquisition!".format("Spanish", "Nobody")
+      'Nobody expects the Spanish Inquisition!'
 
    See :ref:`formatstrings` for a description of the various formatting options
    that can be specified in format strings.