Show an overridden ToString() in the default repr of .NET objects

src/runtime/Types/ClassBase.cs

@@ -379,7 +379,31 @@ public static NewReference tp_repr(BorrowedReference ob)
                 using var args = Runtime.PyTuple_New(1);
                 Runtime.PyTuple_SetItem(args.Borrow(), 0, ob);
                 using var reprFunc = Runtime.PyObject_GetAttr(Runtime.PyBaseObjectType, PyIdentifier.__repr__);
-                return Runtime.PyObject_Call(reprFunc.Borrow(), args.Borrow(), null);
+                var defaultRepr = Runtime.PyObject_Call(reprFunc.Borrow(), args.Borrow(), null);
+                if (defaultRepr.IsNull() || instType.GetMethod("ToString", Type.EmptyTypes)?.DeclaringType == typeof(object))
+                {
+                    return defaultRepr;
+                }
+
+                // like IronPython, show an overridden ToString() so containers of .NET objects print readably:
+                // <QuantConnect.Symbol object at 0x7f9b74b40608 [SPY]>
+                string text;
+                try
+                {
+                    text = co.inst.ToString();
+                }
+                catch (Exception)
+                {
+                    // repr() used to succeed for types whose ToString() throws, keep it that way
+                    return defaultRepr;
+                }
+                if (text is null)
+                {
+                    return defaultRepr;
+                }
+                var defaultReprString = Runtime.GetManagedString(defaultRepr.Borrow());
+                defaultRepr.Dispose();
+                return Runtime.PyString_FromString($"{defaultReprString.Substring(0, defaultReprString.Length - 1)} [{text}]>");
             }
             catch (Exception e)
             {

src/testing/ReprTest.cs

@@ -68,6 +68,22 @@ public class Baz : BazMiddle
 
         }
 
+        public class NullToString
+        {
+            public override string ToString()
+            {
+                return null;
+            }
+        }
+
+        public class ThrowingToString
+        {
+            public override string ToString()
+            {
+                throw new InvalidOperationException("ToString() failed");
+            }
+        }
+
         public class Quux
         {
             public string ToString(string format)

tests/test_repr.py

@@ -18,12 +18,38 @@ def test_system_string():
     ob = System.String("hello")
     assert str(ob) == "hello"
     assert "<System.String object at " in ob.__repr__()
+    assert ob.__repr__().endswith(" [hello]>")
 
 def test_str_only():
     """Test class implementing ToString() but not __repr__()"""
     ob = ReprTest.Bar()
     assert str(ob) == "I implement ToString() but not __repr__()!"
     assert "<Python.Test.Bar object at " in ob.__repr__()
+    assert ob.__repr__().endswith(" [I implement ToString() but not __repr__()!]>")
+
+def test_str_only_nested_in_list():
+    """Test containers show the ToString() of elements implementing ToString() but not __repr__()"""
+    obs = [ReprTest.Bar(), ReprTest.Bar()]
+    assert str(obs).count("[I implement ToString() but not __repr__()!]>") == 2
+
+def test_no_tostring_override():
+    """Test object not overriding ToString() keeps the default repr"""
+    ob = System.Object()
+    assert repr(ob).startswith("<System.Object object at ")
+    assert repr(ob).endswith(">")
+    assert "[" not in repr(ob)
+
+def test_tostring_returns_null():
+    """Test class whose ToString() returns null"""
+    ob = ReprTest.NullToString()
+    assert "<Python.Test.NullToString object at " in repr(ob)
+    assert "[" not in repr(ob)
+
+def test_tostring_throws():
+    """Test class whose ToString() throws"""
+    ob = ReprTest.ThrowingToString()
+    assert "<Python.Test.ThrowingToString object at " in repr(ob)
+    assert "[" not in repr(ob)
 
 def test_hierarchy1():
     """Test inheritance hierarchy with base & middle class implementing ToString"""
@@ -34,10 +60,12 @@ def test_hierarchy1():
     ob2 = ReprTest.BazMiddle()
     assert str(ob2) == "Middle class implementing ToString()!"
     assert "<Python.Test.BazMiddle object at " in ob2.__repr__()
+    assert ob2.__repr__().endswith(" [Middle class implementing ToString()!]>")
 
     ob3 = ReprTest.Baz()
     assert str(ob3) == "Middle class implementing ToString()!"
     assert "<Python.Test.Baz object at " in ob3.__repr__()
+    assert ob3.__repr__().endswith(" [Middle class implementing ToString()!]>")
 
 def bad_tostring():
     """Test ToString that can't be used by str()"""