Tighten example code.

Doc/library/itertools.rst

@@ -381,7 +381,7 @@ loops that truncate the stream.
                 for i in reversed(range(r)):
                     cycles[i] -= 1
                     if cycles[i] == 0:
-                        indices[:] = indices[:i] + indices[i+1:] + indices[i:i+1]
+                        indices[i:] = indices[i+1:] + indices[i:i+1]
                         cycles[i] = n - i
                     else:
                         j = cycles[i]