Index: Lib/optparse.py
===================================================================
--- Lib/optparse.py	(revision 67183)
+++ Lib/optparse.py	(working copy)
@@ -1146,6 +1146,9 @@
         have defined custom types; see SF bug #955889.)  Set it to false
         to restore the behaviour of Optik 1.4.1 and earlier.
 
+      error_log : file
+        if given, errors will be logged to this file instead of stderr
+
       rargs : [string]
         the argument list currently being parsed.  Only set when
         parse_args() is active, and continually trimmed down as
@@ -1178,7 +1181,8 @@
                  formatter=None,
                  add_help_option=True,
                  prog=None,
-                 epilog=None):
+                 epilog=None,
+                 error_log=None):
         OptionContainer.__init__(
             self, option_class, conflict_handler, description)
         self.set_usage(usage)
@@ -1191,6 +1195,9 @@
         self.formatter = formatter
         self.formatter.set_parser(self)
         self.epilog = epilog
+        if error_log is None:
+            error_log = sys.stderr
+        self.error_log = error_log
 
         # Populate the option list; initial sources are the
         # standard_option_list class attribute, the 'option_list'
@@ -1353,7 +1360,7 @@
 
         Parse the command-line options found in 'args' (default:
         sys.argv[1:]).  Any errors result in a call to 'error()', which
-        by default prints the usage message to stderr and calls
+        by default prints the usage message to the error log and calls
         sys.exit() with an error message.  On success returns a pair
         (values, args) where 'values' is an Values instance (with all
         your option values) and 'args' is the list of arguments left
@@ -1550,17 +1557,17 @@
 
     def exit(self, status=0, msg=None):
         if msg:
-            sys.stderr.write(msg)
+            self.error_log.write(msg)
         sys.exit(status)
 
     def error(self, msg):
         """error(msg : string)
 
-        Print a usage message incorporating 'msg' to stderr and exit.
+        Print a usage message incorporating 'msg' to error_log and exit.
         If you override this in a subclass, it should not return -- it
         should either exit or raise an exception.
         """
-        self.print_usage(sys.stderr)
+        self.print_usage(self.error_log)
         self.exit(2, "%s: error: %s\n" % (self.get_prog_name(), msg))
 
     def get_usage(self):
Index: Lib/test/test_optparse.py
===================================================================
--- Lib/test/test_optparse.py	(revision 67183)
+++ Lib/test/test_optparse.py	(working copy)
@@ -1630,6 +1630,29 @@
                              "option -l: invalid long integer value: '0x12x'")
 
 
+class TestErrorLog(BaseTest):
+    def setUp(self):
+        self.log = StringIO()
+        self.parser = OptionParser(error_log=self.log)
+        self.parser.add_option('-f')
+
+    def test_no_output_when_successful(self):
+        self.parser.parse_args(['-f', 'foo'])
+        self.assertEqual('', self.log.getvalue())
+
+    def test_log_on_failure(self):
+        try:
+            self.parser.parse_args(['--fail'])
+        except SystemExit:
+            pass
+        expect = \
+"""Usage: test_optparse.py [options]
+
+test_optparse.py: error: no such option: --fail
+"""
+        self.assertEqual(expect, self.log.getvalue())
+
+
 def test_main():
     test_support.run_unittest(__name__)