diff -r 1267d64c14b3 Lib/sre_parse.py
--- a/Lib/sre_parse.py	Thu Nov 01 14:52:03 2012 +0200
+++ b/Lib/sre_parse.py	Thu Nov 01 21:46:28 2012 +0200
@@ -580,6 +580,8 @@
                                 break
                             name = name + char
                         group = 1
+                        if not name:
+                            raise error("bad group name")
                         if not isname(name):
                             raise error("bad character in group name")
                     elif sourcematch("="):
@@ -592,6 +594,8 @@
                             if char == ")":
                                 break
                             name = name + char
+                        if not name:
+                            raise error("bad group name")
                         if not isname(name):
                             raise error("bad character in group name")
                         gid = state.groupdict.get(name)
@@ -644,6 +648,8 @@
                             break
                         condname = condname + char
                     group = 2
+                    if not condname:
+                        raise error("bad group name")
                     if isname(condname):
                         condgroup = state.groupdict.get(condname)
                         if condgroup is None:
diff -r 1267d64c14b3 Lib/test/test_re.py
--- a/Lib/test/test_re.py	Thu Nov 01 14:52:03 2012 +0200
+++ b/Lib/test/test_re.py	Thu Nov 01 21:46:28 2012 +0200
@@ -161,11 +161,29 @@
         self.assertEqual(re.sub('x*', '-', 'abxd'), '-a-b-d-')
         self.assertEqual(re.sub('x+', '-', 'abxd'), 'ab-d')
 
+    def test_symbolic_groups(self):
+        re.compile('(?P<a>x)(?P=a)(?(a)y)')
+        re.compile('(?P<a1>x)(?P=a1)(?(a1)y)')
+        self.assertRaises(re.error, re.compile, '(?P<a>)(?P<a>)')
+        self.assertRaises(re.error, re.compile, '(?Px)')
+        self.assertRaises(re.error, re.compile, '(?P=)')
+        self.assertRaises(re.error, re.compile, '(?P=1)')
+        self.assertRaises(re.error, re.compile, '(?P=a.)')
+        self.assertRaises(re.error, re.compile, '(?P<)')
+        self.assertRaises(re.error, re.compile, '(?P<>)')
+        self.assertRaises(re.error, re.compile, '(?P<1>)')
+        self.assertRaises(re.error, re.compile, '(?P<a.>)')
+        self.assertRaises(re.error, re.compile, '(?())')
+        self.assertRaises(re.error, re.compile, '(?(a))')
+        self.assertRaises(re.error, re.compile, '(?(1a))')
+        self.assertRaises(re.error, re.compile, '(?(a.))')
+
     def test_symbolic_refs(self):
         self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<a', 'xx')
         self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<', 'xx')
         self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g', 'xx')
         self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<a a>', 'xx')
+        self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<>', 'xx')
         self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<1a1>', 'xx')
         self.assertRaises(IndexError, re.sub, '(?P<a>x)', '\g<ab>', 'xx')
         self.assertRaises(re.error, re.sub, '(?P<a>x)|(?P<b>y)', '\g<b>', 'xx')