python#13899: merge with 3.2.

Lib/sre_parse.py

@@ -245,7 +245,7 @@ def _class_escape(source, escape):
     if code:
         return code
     code = CATEGORIES.get(escape)
-    if code:
+    if code and code[0] == IN:
         return code
     try:
         c = escape[1:2]

Lib/test/test_re.py

@@ -949,6 +949,12 @@ def test_compile(self):
         # Test behaviour when not given a string or pattern as parameter
         self.assertRaises(TypeError, re.compile, 0)
 
+    def test_bug_13899(self):
+        # Issue #13899: re pattern r"[\A]" should work like "A" but matches
+        # nothing. Ditto B and Z.
+        self.assertEqual(re.findall(r'[\A\B\b\C\Z]', 'AB\bCZ'),
+                         ['A', 'B', '\b', 'C', 'Z'])
+
     @bigmemtest(size=_2G, memuse=1)
     def test_large_search(self, size):
         # Issue #10182: indices were 32-bit-truncated.

Misc/NEWS

@@ -144,6 +144,9 @@ Library
 
 - Issue #16900: Issue a ResourceWarning when an ssl socket is left unclosed.
 
+- Issue #13899: \A, \Z, and \B now correctly match the A, Z, and B literals
+  when used inside character classes (e.g. '[\A]').  Patch by Matthew Barnett.
+
 - Issue #15545: Fix regression in sqlite3's iterdump method where it was
   failing if the connection used a row factory (such as sqlite3.Row) that
   produced unsortable objects. (Regression was introduced by fix for 9750).