diff -r 193ac288bc7f Lib/csv.py
--- a/Lib/csv.py	Sat Nov 01 11:05:36 2014 +0200
+++ b/Lib/csv.py	Sat Nov 01 16:58:33 2014 +0200
@@ -231,20 +231,21 @@ class Sniffer:
         quotes = {}
         delims = {}
         spaces = 0
+        groupindex = regexp.groupindex
         for m in matches:
-            n = regexp.groupindex['quote'] - 1
+            n = groupindex['quote'] - 1
             key = m[n]
             if key:
                 quotes[key] = quotes.get(key, 0) + 1
             try:
-                n = regexp.groupindex['delim'] - 1
+                n = groupindex['delim'] - 1
                 key = m[n]
             except KeyError:
                 continue
             if key and (delimiters is None or key in delimiters):
                 delims[key] = delims.get(key, 0) + 1
             try:
-                n = regexp.groupindex['space'] - 1
+                n = groupindex['space'] - 1
             except KeyError:
                 continue
             if m[n]:
diff -r 193ac288bc7f Lib/sre_parse.py
--- a/Lib/sre_parse.py	Sat Nov 01 11:05:36 2014 +0200
+++ b/Lib/sre_parse.py	Sat Nov 01 16:58:33 2014 +0200
@@ -783,6 +783,7 @@ def parse_template(source, pattern):
             del literal[:]
         groups.append((len(literals), index))
         literals.append(None)
+    groupindex = pattern.groupindex
     while True:
         this = sget()
         if this is None:
@@ -806,7 +807,7 @@ def parse_template(source, pattern):
                     if not name.isidentifier():
                         raise error("bad character in group name")
                     try:
-                        index = pattern.groupindex[name]
+                        index = groupindex[name]
                     except KeyError:
                         msg = "unknown group name: {0!r}".format(name)
                         raise IndexError(msg)
diff -r 193ac288bc7f Lib/test/test_re.py
--- a/Lib/test/test_re.py	Sat Nov 01 11:05:36 2014 +0200
+++ b/Lib/test/test_re.py	Sat Nov 01 16:58:33 2014 +0200
@@ -493,6 +493,13 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.match("(a)", "a").regs, ((0, 1), (0, 1)))
         self.assertTrue(re.match("(a)", "a").re)
 
+        # Issue 14260.
+        p = re.compile(r'abc(?P<n>def)')
+        self.assertEqual(sorted(p.groupindex), ["n"])
+        self.assertEqual(p.groupindex["n"], 1)
+        p.groupindex["n"] = 0
+        self.assertEqual(p.groupindex["n"], 1)
+
     def test_special_escapes(self):
         self.assertEqual(re.search(r"\b(b.)\b",
                                    "abcd abc bcd bx").group(1), "bx")
diff -r 193ac288bc7f Modules/_sre.c
--- a/Modules/_sre.c	Sat Nov 01 11:05:36 2014 +0200
+++ b/Modules/_sre.c	Sat Nov 01 16:58:33 2014 +0200
@@ -1371,12 +1371,24 @@ static PyMethodDef pattern_methods[] = {
     {NULL, NULL}
 };
 
+/* PatternObject's 'groupindex' method. */
+static PyObject *
+pattern_groupindex(PatternObject *self)
+{
+    return PyDict_Copy(self->groupindex);
+}
+
+static PyGetSetDef pattern_getset[] = {
+    {"groupindex", (getter)pattern_groupindex, (setter)NULL,
+      "A dictionary mapping group names to group numbers."},
+    {NULL}  /* Sentinel */
+};
+
 #define PAT_OFF(x) offsetof(PatternObject, x)
 static PyMemberDef pattern_members[] = {
     {"pattern",    T_OBJECT,    PAT_OFF(pattern),       READONLY},
     {"flags",      T_INT,       PAT_OFF(flags),         READONLY},
     {"groups",     T_PYSSIZET,  PAT_OFF(groups),        READONLY},
-    {"groupindex", T_OBJECT,    PAT_OFF(groupindex),    READONLY},
     {NULL}  /* Sentinel */
 };
 
@@ -1409,6 +1421,7 @@ static PyTypeObject Pattern_Type = {
     0,                                  /* tp_iternext */
     pattern_methods,                    /* tp_methods */
     pattern_members,                    /* tp_members */
+    pattern_getset,                     /* tp_getset */
 };
 
 static int _validate(PatternObject *self); /* Forward */