From e670b2d5c39ce6ac72890e52e9d505f90c33ccba Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Tue, 22 Nov 2016 15:23:00 +0100
Subject: [PATCH 1/2] Issue #28727: Fix typo in pattern_richcompare()

Typo catched by Serhiy Storchaka, thanks!
---
 Modules/_sre.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/_sre.c b/Modules/_sre.c
index c1e9fa6e6bd..1b7741696d0 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -2688,7 +2688,7 @@ pattern_richcompare(PyObject *lefto, PyObject *righto, int op)
 
     cmp = (left->flags == right->flags
            && left->isbytes == right->isbytes
-           && left->codesize && right->codesize);
+           && left->codesize == right->codesize);
     if (cmp) {
         /* Compare the code and the pattern because the same pattern can
            produce different codes depending on the locale used to compile the

From bcf4dccfa77df6fd75181e2a7cbfbf2d4b2c6255 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Tue, 22 Nov 2016 15:30:38 +0100
Subject: [PATCH 2/2] Issue #28727: Optimize pattern_richcompare() for a==a

A pattern is equal to itself.
---
 Lib/test/test_re.py | 4 ++++
 Modules/_sre.c      | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index 4fcd2d463dc..84131d2b926 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -1781,6 +1781,10 @@ SUBPATTERN None 0 0
     def test_pattern_compare(self):
         pattern1 = re.compile('abc', re.IGNORECASE)
 
+        # equal to itself
+        self.assertEqual(pattern1, pattern1)
+        self.assertFalse(pattern1 != pattern1)
+
         # equal
         re.purge()
         pattern2 = re.compile('abc', re.IGNORECASE)
diff --git a/Modules/_sre.c b/Modules/_sre.c
index 1b7741696d0..979e61fb535 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -2683,6 +2683,12 @@ pattern_richcompare(PyObject *lefto, PyObject *righto, int op)
     if (Py_TYPE(lefto) != &Pattern_Type || Py_TYPE(righto) != &Pattern_Type) {
         Py_RETURN_NOTIMPLEMENTED;
     }
+
+    if (lefto == righto) {
+        /* a pattern is equal to itself */
+        return PyBool_FromLong(op == Py_EQ);
+    }
+
     left = (PatternObject *)lefto;
     right = (PatternObject *)righto;