Fixed bug #470582, using a modified version of patch #527371,

from Greg Chapman.

* Modules/_sre.c
  (lastmark_restore): New function, implementing algorithm to restore
  a state to a given lastmark. In addition to the similar algorithm used
  in a few places of SRE_MATCH, restore lastindex when restoring lastmark.
  (SRE_MATCH): Replace lastmark inline restoring by lastmark_restore(),
  function. Also include it where missing. In SRE_OP_MARK, set lastindex
  only if i > lastmark.

* Lib/test/re_tests.py
* Lib/test/test_sre.py
  Included regression tests for the fixed bugs.

* Misc/NEWS
  Mention fixes.

1 files changed, 7 insertions, 0 deletions

diff --git a/Misc/NEWS b/Misc/NEWS
index c57ca1d..cccaff5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -352,6 +352,13 @@ Extension modules
   to the value of the PYTHON_API_VERSION macro with which the
   interpreter was compiled.
 
+- Fixed bug #470582: sre module would return a tuple (None, 'a', 'ab')
+  when applying the regular expression '^((a)c)?(ab)$' on 'ab'. It now
+  returns (None, None, 'ab'), as expected. Also fixed handling of
+  lastindex/lastgroup match attributes in a similar cases. For example,
+  when running the expression r'(a)(b)?b' over 'ab', lastindex must be
+  1, not 2.
+
 Library
 -------