diff --git a/Lib/string.py b/Lib/string.py
index 4599997..5089193 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))
 
 
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