QuantConnect · jhonabreul · Aug 12, 2026 · Aug 11, 2026 · Aug 11, 2026 · Aug 11, 2026
diff --git a/src/runtime/MethodBinder.cs b/src/runtime/MethodBinder.cs
@@ -1052,6 +1052,14 @@ internal virtual NewReference Invoke(BorrowedReference inst, BorrowedReference a
                             }
                             value.Append(' ').Append(overloads);
                         }
+
+                        // After the overloads block: consumers that extract the hint from
+                        // its marker onwards must keep this line too.
+                        var mismatch = DiagnoseClosestOverloadMismatch(candidates, args, kw);
+                        if (mismatch.Length > 0)
+                        {
+                            value.Append('\n').Append(mismatch);
+                        }
                     }
                     catch
                     {
@@ -1061,14 +1069,6 @@ internal virtual NewReference Invoke(BorrowedReference inst, BorrowedReference a
                         Exceptions.Clear();
                     }
 
-                    // After the overloads block: consumers that extract the hint from
-                    // its marker onwards must keep this line too.
-                    var mismatch = DiagnoseClosestOverloadMismatch(candidates, args, kw);
-                    if (mismatch.Length > 0)
-                    {
-                        value.Append('\n').Append(mismatch);
-                    }
-
                     Exceptions.RaiseTypeError(value.ToString());
                 }
 

diff --git a/src/runtime/Types/ClassBase.cs b/src/runtime/Types/ClassBase.cs
@@ -49,7 +49,7 @@ private enum SuggestionKind
         // getattr(self, "_optional", None) on a .NET-derived object, or a mistyped enum value).
         // Memoize the fully-built " Did you mean: ...?" hint (empty when there is nothing to
         // suggest) per (type, missing-name) so repeats are a dictionary lookup instead of an
-        // O(members) reflection + Levenshtein scan on every miss.
+        // O(members) reflection + similarity scan on every miss.
         private static readonly ConcurrentDictionary<(Type Type, string Name), string> _suggestionCache = new();
 
         internal ClassBase(Type tp)
@@ -837,21 +837,31 @@ private static Dictionary<string, SuggestionKind> GetCandidateMemberNames(Type t
         // Builds the " Did you mean: 'x', 'y'?" hint for a missing attribute, or an empty
         // string when no member is similar enough to suggest. The result is cached in
         // _suggestionCache, so this runs at most once per (type, missing-name).
+        //
+        // Jaro-Winkler (prefix-favoring) keeps suffix-extended targets that an edit-distance
+        // cutoff rejects (InteractiveBrokers -> INTERACTIVE_BROKERS_BROKERAGE); gated
+        // containment covers fragment lookups outside its match window ('cash' -> 'set_cash').
         private static string ComputeSimilarMemberNames(Type type, string name)
         {
             const int MaxSuggestions = 5;
-            var threshold = Math.Max(2, name.Length / 3);
+            // In evaluation over real member sets, intended targets scored >= 0.90 and noise <= 0.85.
+            const double SimilarityThreshold = 0.87;
 
-            var scored = new List<(string Name, int Distance, SuggestionKind Kind)>();
+            var scored = new List<(string Name, double Score, SuggestionKind Kind)>();
             foreach (var candidate in GetCandidateMemberNames(type))
             {
-                var distance = Util.LevenshteinDistance(name, candidate.Key);
-                var related = distance <= threshold
-                    || candidate.Key.IndexOf(name, StringComparison.OrdinalIgnoreCase) >= 0
-                    || name.IndexOf(candidate.Key, StringComparison.OrdinalIgnoreCase) >= 0;
-                if (related)
+                var score = Util.JaroWinklerSimilarity(name, candidate.Key);
+                if (score < SimilarityThreshold)
                 {
-                    scored.Add((candidate.Key, distance, candidate.Value));
+                    // Coverage scoring ranks containment matches below any similarity match.
+                    score = IsMeaningfulContainment(name, candidate.Key)
+                        ? (double)Math.Min(name.Length, candidate.Key.Length) / Math.Max(name.Length, candidate.Key.Length)
+                        : 0;
+                }
+
+                if (score > 0)
+                {
+                    scored.Add((candidate.Key, score, candidate.Value));
                 }
             }
 
@@ -861,7 +871,7 @@ private static string ComputeSimilarMemberNames(Type type, string name)
             }
 
             var ordered = scored
-                .OrderBy(t => t.Distance)
+                .OrderByDescending(t => t.Score)
                 .ThenBy(t => t.Name, StringComparer.OrdinalIgnoreCase)
                 .ToList();
 
@@ -895,5 +905,22 @@ private static (string Name, SuggestionKind Kind) ToSnakeCaseMemberName(MemberIn
             };
         }
 
+        // Without the length gates every 1-2 letter member is a substring of any long
+        // missed name and floods the suggestion list.
+        private static bool IsMeaningfulContainment(string name, string candidate)
+        {
+            const int MinFragmentLength = 3;
+
+            if (name.Length >= MinFragmentLength
+                && candidate.IndexOf(name, StringComparison.OrdinalIgnoreCase) >= 0)
+            {
+                return true;
+            }
+
+            return candidate.Length >= MinFragmentLength
+                && 2 * candidate.Length >= name.Length
+                && name.IndexOf(candidate, StringComparison.OrdinalIgnoreCase) >= 0;
+        }
+
     }
 }
diff --git a/src/runtime/Util/Util.cs b/src/runtime/Util/Util.cs
@@ -363,5 +363,91 @@ internal static int LevenshteinDistance(string a, string b)
             }
             return prev[m];
         }
+
+        /// <summary>
+        /// Case-insensitive Jaro-Winkler similarity in [0, 1] (Jaro boosted by shared prefix).
+        /// </summary>
+        internal static double JaroWinklerSimilarity(string a, string b)
+        {
+            const double PrefixScale = 0.1;
+            const int MaxPrefixLength = 4;
+
+            a = a.ToLowerInvariant();
+            b = b.ToLowerInvariant();
+
+            var jaro = JaroSimilarity(a, b);
+
+            var prefix = 0;
+            var maxPrefix = Math.Min(MaxPrefixLength, Math.Min(a.Length, b.Length));
+            while (prefix < maxPrefix && a[prefix] == b[prefix])
+            {
+                prefix++;
+            }
+
+            return jaro + prefix * PrefixScale * (1 - jaro);
+        }
+
+        private static double JaroSimilarity(string a, string b)
+        {
+            if (a == b)
+            {
+                return 1;
+            }
+
+            var n = a.Length;
+            var m = b.Length;
+            if (n == 0 || m == 0)
+            {
+                return 0;
+            }
+
+            var window = Math.Max(0, Math.Max(n, m) / 2 - 1);
+            var aMatched = new bool[n];
+            var bMatched = new bool[m];
+
+            var matches = 0;
+            for (var i = 0; i < n; i++)
+            {
+                var lo = Math.Max(0, i - window);
+                var hi = Math.Min(m, i + window + 1);
+                for (var j = lo; j < hi; j++)
+                {
+                    if (!bMatched[j] && a[i] == b[j])
+                    {
+                        aMatched[i] = bMatched[j] = true;
+                        matches++;
+                        break;
+                    }
+                }
+            }
+
+            if (matches == 0)
+            {
+                return 0;
+            }
+
+            var transpositions = 0;
+            var k = 0;
+            for (var i = 0; i < n; i++)
+            {
+                if (!aMatched[i])
+                {
+                    continue;
+                }
+                while (!bMatched[k])
+                {
+                    k++;
+                }
+                if (a[i] != b[k])
+                {
+                    transpositions++;
+                }
+                k++;
+            }
+            transpositions /= 2;
+
+            return ((double)matches / n + (double)matches / m
+                + (double)(matches - transpositions) / matches) / 3;
+        }
     }
 }
diff --git a/src/testing/classtest.cs b/src/testing/classtest.cs
@@ -86,5 +86,31 @@ public static int[] CalculationResults()
         }
 
         public static int CalculationResult { get; set; }
+
+        // Short members, all substrings of a longer miss like 'set_account_type', which
+        // must not suggest them.
+        public static int T()
+        {
+            return 0;
+        }
+
+        public static int CC()
+        {
+            return 0;
+        }
+
+        public static void SetAccountCurrency(string currency)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Supports suggestion tests for enum members that extend the guessed name with a suffix.
+    /// </summary>
+    public enum SuggestionEnum
+    {
+        InteractiveBrokersBrokerage,
+        InteractiveBrokersFix,
+        Binance,
     }
 }
diff --git a/tests/test_class.py b/tests/test_class.py
@@ -211,6 +211,40 @@ def test_missing_property_suggests_data_only():
     assert "'calculation_results'" not in hint
 
 
+def _suggestions(message):
+    """Extract the quoted member names from a "Did you mean" hint."""
+    import re
+    return re.findall(r"'([^']+)'", message.split("Did you mean")[1])
+
+
+def test_missing_attribute_does_not_suggest_short_members():
+    """A long missed name must not collect 1-2 letter members via substring containment.
+
+    Every short member is a substring of a long miss, so hints used to read
+    "Did you mean: 'cc', 'co', 'a', 'c', 't'?" while the intended member was absent.
+    """
+    from Python.Test import SuggestionTest
+
+    with pytest.raises(AttributeError) as exc_info:
+        _ = SuggestionTest.set_account_type
+
+    message = str(exc_info.value)
+    assert "Did you mean" in message
+    suggested = _suggestions(message)
+    assert "set_account_currency" in suggested
+    assert all(len(s) > 2 for s in suggested)
+
+
+def test_missing_attribute_fragment_suggests_containing_member():
+    """Typing a meaningful fragment of a member name still suggests that member."""
+    from Python.Test import SuggestionTest
+
+    with pytest.raises(AttributeError) as exc_info:
+        _ = SuggestionTest.currency
+
+    assert "set_account_currency" in _suggestions(str(exc_info.value))
+
+
 def test_missing_static_member_no_similar():
     """A static member with no similar name keeps the standard message (no hint)."""
     from System import Math

diff --git a/tests/test_enum.py b/tests/test_enum.py
@@ -68,6 +68,24 @@ def test_missing_enum_member_hasattr_still_false():
     assert not hasattr(DayOfWeek, "Sundey")
 
 
+def test_missing_enum_member_suffix_extended_name_suggested():
+    """A guessed name that the real member extends with a suffix must be suggested,
+    from both the PascalCase and the UPPER_SNAKE spelling of the guess."""
+    import re
+    from Python.Test import SuggestionEnum
+
+    for miss in ("InteractiveBrokers", "INTERACTIVE_BROKERS"):
+        with pytest.raises(AttributeError) as exc_info:
+            getattr(SuggestionEnum, miss)
+
+        message = str(exc_info.value)
+        assert "Did you mean" in message
+        suggested = re.findall(r"'([^']+)'", message.split("Did you mean")[1])
+        assert "INTERACTIVE_BROKERS_BROKERAGE" in suggested
+        assert "INTERACTIVE_BROKERS_FIX" in suggested
+        assert "BINANCE" not in suggested
+
+
 def test_byte_enum():
     """Test byte enum."""
     assert Test.ByteEnum.Zero == Test.ByteEnum(0)