Note default values for namedtuple extra args.

Doc/library/collections.rst

@@ -566,7 +566,7 @@ Named tuples assign meaning to each position in a tuple and allow for more reada
 self-documenting code.  They can be used wherever regular tuples are used, and
 they add the ability to access fields by name instead of position index.
 
-.. function:: namedtuple(typename, field_names, [verbose], [rename])
+.. function:: namedtuple(typename, field_names, [verbose=False], [rename=False])
 
    Returns a new tuple subclass named *typename*.  The new subclass is used to
    create tuple-like objects that have fields accessible by attribute lookup as