gh-132449: Improve the algorithm to detect typos in keywords (#132837)

Author: pablogsal

Lib/test/test_syntax.py

@@ -1838,6 +1838,12 @@
 Traceback (most recent call last):
 SyntaxError: invalid syntax. Did you mean 'for'?
 
+
+>>> for x im n:
+...     pass
+Traceback (most recent call last):
+SyntaxError: invalid syntax. Did you mean 'in'?
+
 >>> f(a=23, a=234)
 Traceback (most recent call last):
    ...

Lib/traceback.py

@@ -1339,10 +1339,14 @@ def _find_keyword_typos(self):
             if tokens_left_to_process < 0:
                 break
             # Limit the number of possible matches to try
-            matches = difflib.get_close_matches(wrong_name, keyword.kwlist, n=3)
-            if not matches and _suggestions is not None:
+            max_matches = 3
+            matches = []
+            if _suggestions is not None:
                 suggestion = _suggestions._generate_suggestions(keyword.kwlist, wrong_name)
-                matches = [suggestion] if suggestion is not None else matches
+                if suggestion:
+                    matches.append(suggestion)
+            matches.extend(difflib.get_close_matches(wrong_name, keyword.kwlist, n=max_matches, cutoff=0.5))
+            matches = matches[:max_matches]
             for suggestion in matches:
                 if not suggestion or suggestion == wrong_name:
                     continue