Port parsing fallback from evaluation to rewards

src/maxtext/trainers/post_train/rl/utils_rl.py

@@ -229,7 +229,16 @@ def check_answer(prompts, completions, answer, tmvp_config, **kargs):
   value.
   """
   match_format = get_match_format_regex(tmvp_config)
-  extracted_responses = [guess.group(1) if (guess := match_format.search(c)) is not None else None for c in completions]
+  answer_fallback = get_answer_fallback_regex(tmvp_config)
+
+  extracted_responses = []
+  for c in completions:
+    full_match = match_format.search(c)
+    if full_match is not None:
+      extracted_responses.append(full_match.group(1))
+    else:
+      fallback_matches = answer_fallback.findall(c)
+      extracted_responses.append(fallback_matches[-1].strip() if fallback_matches else None)
 
   scores = []
   for guess, true_answer in zip(extracted_responses, answer):
@@ -408,7 +417,16 @@ def check_numbers(prompts, completions, answer, tmvp_config, **kargs):
 
   # Extract full answer content from solution tags (not just first number)
   match_format = get_match_format_regex(tmvp_config)
-  extracted_responses = [guess.group(1) if (guess := match_format.search(c)) is not None else None for c in completions]
+  answer_fallback = get_answer_fallback_regex(tmvp_config)
+
+  extracted_responses = []
+  for c in completions:
+    full_match = match_format.search(c)
+    if full_match is not None:
+      extracted_responses.append(full_match.group(1))
+    else:
+      fallback_matches = answer_fallback.findall(c)
+      extracted_responses.append(fallback_matches[-1].strip() if fallback_matches else None)
 
   scores = []
   if tmvp_config.debug.rl:

tests/post_training/unit/rl_utils_test.py

@@ -236,12 +236,12 @@ def test_extraction_fails_no_tags(self):
 
   @pytest.mark.cpu_only
   def test_extraction_fails_answer_tags_only(self):
-    """<answer> tag alone (no <reasoning> block) is not matched by the regex, score 0."""
+    """<answer> tag alone (no <reasoning> block) is matched by the regex as a fallback, score 1.5."""
     scores = self._check(
         completions=["<answer>42</answer>"],
         answer=["42"],
     )
-    self.assertEqual(scores[0], 0)
+    self.assertEqual(scores[0], 1.5)
 
   @pytest.mark.cpu_only
   def test_extraction_fails_reasoning_tags_only(self):