diff -r ddcf09a348ca Lib/test/test_warnings.py
--- a/Lib/test/test_warnings.py	Wed Nov 28 19:24:44 2012 +0200
+++ b/Lib/test/test_warnings.py	Thu Nov 29 03:13:56 2012 +0100
@@ -384,12 +384,13 @@
     def test_improper_input(self):
         # Uses the private _setoption() function to test the parsing
         # of command-line warning arguments
+        self.module.resetwarnings()
         with original_warnings.catch_warnings(module=self.module):
-            self.assertRaises(self.module._OptionError,
+            self.assertRaises(self.module.WarningsOptParsingError,
                               self.module._setoption, '1:2:3:4:5:6')
-            self.assertRaises(self.module._OptionError,
+            self.assertRaises(self.module.WarningsOptParsingError,
                               self.module._setoption, 'bogus::Warning')
-            self.assertRaises(self.module._OptionError,
+            self.assertRaises(self.module.WarningsOptParsingError,
                               self.module._setoption, 'ignore:2::4:-5')
             self.module._setoption('error::Warning::0')
             self.assertRaises(UserWarning, self.module.warn, 'convert to error')
@@ -410,6 +411,19 @@
         self.assertFalse(out.strip())
         self.assertNotIn(b'RuntimeWarning', err)
 
+    def test_cmd_line_API(self):
+        # check if the opt args are properly parsed
+        self.module.resetwarnings()
+        with original_warnings.catch_warnings(module=self.module):
+            self.assertRaises(self.module.WarningsOptParsingError,
+                              self.module.process_option, '1:2:3:4:5:6')
+            self.assertRaises(self.module.WarningsOptParsingError,
+                              self.module.process_option, 'bogus::Warning')
+            self.assertRaises(self.module.WarningsOptParsingError,
+                              self.module.process_option, 'ignore:2::4:-5')
+            self.module.process_option('error::Warning::0')
+            self.assertRaises(UserWarning, self.module.warn, 'convert to error')
+
 class CWCmdLineTests(BaseTest, WCmdLineTests):
     module = c_warnings
 
diff -r ddcf09a348ca Lib/warnings.py
--- a/Lib/warnings.py	Wed Nov 28 19:24:44 2012 +0200
+++ b/Lib/warnings.py	Thu Nov 29 03:13:56 2012 +0100
@@ -81,15 +81,29 @@
     filters[:] = []
 
 class _OptionError(Exception):
+    """Exception used by option processing helpers.
+    Kept for compatibility"""
+    pass
+
+
+class WarningsOptParsingError(_OptionError):
     """Exception used by option processing helpers."""
     pass
 
+
+def process_option(opt):
+    """Parse a comma separated warning filter defintion and insert it.
+    The filter definition must match python -W option format
+    """
+    # let the exceptions rise to the user
+    _setoption(opt)
+
 # Helper to process -W options passed via sys.warnoptions
 def _processoptions(args):
     for arg in args:
         try:
             _setoption(arg)
-        except _OptionError as msg:
+        except WarningsOptParsingError as msg:
             print("Invalid -W option ignored:", msg, file=sys.stderr)
 
 # Helper for _processoptions()
@@ -97,7 +111,7 @@
     import re
     parts = arg.split(':')
     if len(parts) > 5:
-        raise _OptionError("too many fields (max 5): %r" % (arg,))
+        raise WarningsOptParsingError("too many fields (max 5): %r" % (arg,))
     while len(parts) < 5:
         parts.append('')
     action, message, category, module, lineno = [s.strip()
@@ -114,7 +128,7 @@
             if lineno < 0:
                 raise ValueError
         except (ValueError, OverflowError):
-            raise _OptionError("invalid lineno %r" % (lineno,))
+            raise WarningsOptParsingError("invalid lineno %r" % (lineno,))
     else:
         lineno = 0
     filterwarnings(action, message, category, module, lineno)
@@ -127,7 +141,7 @@
     for a in ('default', 'always', 'ignore', 'module', 'once', 'error'):
         if a.startswith(action):
             return a
-    raise _OptionError("invalid action: %r" % (action,))
+    raise WarningsOptParsingError("invalid action: %r" % (action,))
 
 # Helper for _setoption()
 def _getcategory(category):
@@ -138,7 +152,8 @@
         try:
             cat = eval(category)
         except NameError:
-            raise _OptionError("unknown warning category: %r" % (category,))
+            raise WarningsOptParsingError("unknown warning category: %r" %
+                                          (category,))
     else:
         i = category.rfind(".")
         module = category[:i]
@@ -146,13 +161,15 @@
         try:
             m = __import__(module, None, None, [klass])
         except ImportError:
-            raise _OptionError("invalid module name: %r" % (module,))
+            raise WarningsOptParsingError("invalid module name: %r" % (module,))
         try:
             cat = getattr(m, klass)
         except AttributeError:
-            raise _OptionError("unknown warning category: %r" % (category,))
+            raise WarningsOptParsingError("unknown warning category: %r" %
+                                          (category,))
     if not issubclass(cat, Warning):
-        raise _OptionError("invalid warning category: %r" % (category,))
+        raise WarningsOptParsingError("invalid warning category: %r" %
+                                      (category,))
     return cat