Add an example.

pep-0237.txt

@@ -205,6 +205,30 @@ Transition
     B4. Python 3.0 (at least two years in the future).
 
 
+Example
+
+    If you pass a long int to a C function or built-in operation that
+    takes an integer, it will be treated the same as as a short int as
+    long as the value fits (by virtue of how PyArg_ParseTuple() is
+    implemented).  If the long value doesn't fit, it will still raise
+    an OverflowError.  For example:
+
+      def fact(n):
+          if n <= 1:
+              return 1
+          return n*fact(n-1)
+
+      A = "ABCDEFGHIJKLMNOPQ"
+      n = input("Gimme an int: ")
+      print A[fact(n)%17]
+
+    For n >= 13, this currently raises OverflowError (unless the user
+    enters a trailing 'L' as part of their input), even though the
+    calculated index would always be in range(17).  With the new
+    approach this code will do the right thing: the index will be
+    calculated as a long int, but its value will be in range.
+
+
 Open Issues
 
     We expect that these issues will be resolved over time, as more