Don't include unnamed groups in groupdict (#1524)

Author: slozier

Src/IronPython.Modules/re.cs

@@ -748,23 +748,25 @@ static string ValidateString(object? str) {
                 void AppendGroup(StringBuilder sb, int index) => sb.Append(_m.Groups[index].Value);
             }
 
-            private static bool IsGroupNumber(string name) {
-                foreach (char c in name) {
-                    if (!char.IsNumber(c)) return false;
-                }
-                return true;
-            }
-
             [return: DictionaryTypeInfo(typeof(string), typeof(object))]
             public PythonDictionary groupdict(object? @default = null) {
                 string[] groupNames = this.re._re.GetGroupNames();
                 Debug.Assert(groupNames.Length == this._m.Groups.Count);
                 PythonDictionary d = new PythonDictionary();
                 for (int i = 0; i < groupNames.Length; i++) {
-                    if (IsGroupNumber(groupNames[i])) continue; // python doesn't report group numbers
-                    d[groupNames[i]] = re.GetGroupValue(_m.Groups[i], @default);
+                    var groupName = groupNames[i];
+                    if (IsGroupNumber(groupName)) continue; // python doesn't report group numbers
+                    if (groupName.StartsWith(_mangledNamedGroup, StringComparison.Ordinal)) continue; // don't include unnamed groups
+                    d[groupName] = re.GetGroupValue(_m.Groups[i], @default);
                 }
                 return d;
+
+                static bool IsGroupNumber(string name) {
+                    foreach (char c in name) {
+                        if (!char.IsNumber(c)) return false;
+                    }
+                    return true;
+                }
             }
 
             [return: SequenceTypeInfo(typeof(int))]

Tests/modules/io_related/test_re.py

@@ -836,4 +836,10 @@ def test_pos_endpos(self):
         for m2 in (p.finditer("a", -100), p.finditer("a", -100, 100), p.finditer("a", endpos=100)):
             self.assertEqual(m.span(), next(m2).span())
 
+    def test_ipy2_gh821(self):
+        # https://github.com/IronLanguages/ironpython2/issues/821
+        # don't include unnamed groups in groupdict
+        d = re.match('(?P<foo>.*)(.*)', 'bar').groupdict()
+        self.assertEqual(d, {'foo': 'bar'})
+
 run_test(__name__)