diff --git a/Lib/string.py b/Lib/string.py
index e071a2d..a9898e8 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -29,15 +29,17 @@
 
 # Capitalize the words in a string, e.g. " aBc  dEf " -> "Abc Def".
 def capwords(s, sep=None):
-    """capwords(s, [sep]) -> string
+    """capwords(s [,sep]) -> string
 
     Split the argument into words using split, capitalize each
     word using capitalize, and join the capitalized words using
-    join. Note that this replaces runs of whitespace characters by
-    a single space.
+    join.  If the optional second argument sep is absent or None,
+    runs of whitespace characters are replaced by a single space
+    and leading and trailing whitespace are removed, otherwise
+    sep is used to split and join the words.
 
     """
-    return (sep or ' ').join([x.capitalize() for x in s.split(sep)])
+    return (sep or ' ').join(x.capitalize() for x in s.split(sep))
 
 
 # Construct a translation map for bytes.translate
diff --git a/Lib/test/test_string.py b/Lib/test/test_string.py
index 743fa6b..b495d69 100644
--- a/Lib/test/test_string.py
+++ b/Lib/test/test_string.py
@@ -22,6 +22,9 @@
         self.assertEqual(string.capwords('ABC DEF GHI'), 'Abc Def Ghi')
         self.assertEqual(string.capwords('ABC-DEF-GHI', '-'), 'Abc-Def-Ghi')
         self.assertEqual(string.capwords('ABC-def DEF-ghi GHI'), 'Abc-def Def-ghi Ghi')
+        self.assertEqual(string.capwords('   aBc  DeF   '), 'Abc Def')
+        self.assertEqual(string.capwords('\taBc\tDeF\t'), 'Abc Def')
+        self.assertEqual(string.capwords('\taBc\tDeF\t', '\t'), '\tAbc\tDef\t')
 
     def test_formatter(self):
         fmt = string.Formatter()