#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.

Lib/sre_parse.py

@@ -235,7 +235,7 @@ 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

@@ -857,6 +857,12 @@ class ReTests(unittest.TestCase):
         # 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=character_size)
     def test_large_search(self, size):
         # Issue #10182: indices were 32-bit-truncated.

Misc/ACKS

@@ -65,6 +65,7 @@ Chris Barker
 Anton Barkovsky
 Nick Barnes
 Quentin Barnes
+Matthew Barnett
 Richard Barran
 Cesar Eduardo Barros
 Des Barry

Misc/NEWS

@@ -199,6 +199,9 @@ Core and Builtins
 Library
 -------
 
+- 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).