Issue #27177: Match objects in the re module now support index-like objects

as group indices.  Based on patches by Jeroen Demeyer and Xiang Zhang.

Lib/test/test_re.py

@@ -414,19 +414,33 @@ class ReTests(unittest.TestCase):
         self.assertEqual(pat.match('bc').groups(), ('b', None, 'b', 'c'))
         self.assertEqual(pat.match('bc').groups(""), ('b', "", 'b', 'c'))
 
-        # A single group
-        m = re.match('(a)', 'a')
-        self.assertEqual(m.group(0), 'a')
-        self.assertEqual(m.group(0), 'a')
-        self.assertEqual(m.group(1), 'a')
-        self.assertEqual(m.group(1, 1), ('a', 'a'))
-
         pat = re.compile('(?:(?P<a1>a)|(?P<b2>b))(?P<c3>c)?')
         self.assertEqual(pat.match('a').group(1, 2, 3), ('a', None, None))
         self.assertEqual(pat.match('b').group('a1', 'b2', 'c3'),
                          (None, 'b', None))
         self.assertEqual(pat.match('ac').group(1, 'b2', 3), ('a', None, 'c'))
 
+    def test_group(self):
+        class Index:
+            def __init__(self, value):
+                self.value = value
+            def __index__(self):
+                return self.value
+        # A single group
+        m = re.match('(a)(b)', 'ab')
+        self.assertEqual(m.group(), 'ab')
+        self.assertEqual(m.group(0), 'ab')
+        self.assertEqual(m.group(1), 'a')
+        self.assertEqual(m.group(Index(1)), 'a')
+        self.assertRaises(IndexError, m.group, -1)
+        self.assertRaises(IndexError, m.group, 3)
+        self.assertRaises(IndexError, m.group, 1<<1000)
+        self.assertRaises(IndexError, m.group, Index(1<<1000))
+        self.assertRaises(IndexError, m.group, 'x')
+        # Multiple groups
+        self.assertEqual(m.group(2, 1), ('b', 'a'))
+        self.assertEqual(m.group(Index(2), Index(1)), ('b', 'a'))
+
     def test_re_fullmatch(self):
         # Issue 16203: Proposal: add re.fullmatch() method.
         self.assertEqual(re.fullmatch(r"a", "a").span(), (0, 1))

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.6.0 alpha 3
 Library
 -------
 
+- Issue #27177: Match objects in the re module now support index-like objects
+  as group indices.  Based on patches by Jeroen Demeyer and Xiang Zhang.
+
 - Issue #26754: Some functions (compile() etc) accepted a filename argument
   encoded as an iterable of integers. Now only strings and byte-like objects
   are accepted.

Modules/_sre.c

@@ -2049,8 +2049,9 @@ match_getindex(MatchObject* self, PyObject* index)
         /* Default value */
         return 0;
 
-    if (PyLong_Check(index))
+    if (PyIndex_Check(index)) {
-        return PyLong_AsSsize_t(index);
+        return PyNumber_AsSsize_t(index, NULL);
+    }
 
     i = -1;