Marshall out iterables as lists in CPython

src/Libraries/DSCPython/CPythonEvaluator.cs

@@ -195,18 +195,15 @@ public static DataMarshaler OutputMarshaler
                     outputMarshaler.RegisterMarshaler(
                         delegate (PyObject pyObj)
                         {
-                            if (PyList.IsListType(pyObj))
+                            // First, check if we are dealing with a wrapped .NET object.
+                            // This simplifies the cases that come afterwards, as wrapped
+                            // .NET collections pass some Python checks but not others. 
+                            var clrObj = pyObj.GetManagedObject();
+                            if (clrObj != null)
                             {
-                                using (var pyList = new PyList(pyObj))
-                                {
-                                    var list = new List<object>();
-                                    foreach (PyObject item in pyList)
-                                    {
-                                        list.Add(outputMarshaler.Marshal(item));
-                                    }
-                                    return list;
-                                }
+                                return outputMarshaler.Marshal(clrObj);
                             }
+                            // Dictionaries are iterable, so they should come first
                             if (PyDict.IsDictType(pyObj))
                             {
                                 using (var pyDict = new PyDict(pyObj))
@@ -222,6 +219,20 @@ public static DataMarshaler OutputMarshaler
                                     return dict;
                                 }
                             }
+                            // Other iterables should become lists, except for strings
+                            if (PyIter.IsIterable(pyObj) && !PyString.IsStringType(pyObj))
+                            {
+                                using (var pyList = PyList.AsList(pyObj))
+                                {
+                                    var list = new List<object>();
+                                    foreach (PyObject item in pyList)
+                                    {
+                                        list.Add(outputMarshaler.Marshal(item));
+                                    }
+                                    return list;
+                                }
+                            }
+                            // Special case for big long values: decode them as BigInteger
                             if (PyLong.IsLongType(pyObj))
                             {
                                 using (var pyLong = PyLong.AsLong(pyObj))
@@ -236,7 +247,7 @@ public static DataMarshaler OutputMarshaler
                                     }
                                 }
                             }
-
+                            // Default handling for other Python objects
                             var unmarshalled = pyObj.AsManagedObject(typeof(object));
                             if (unmarshalled is PyObject)
                             {

test/Libraries/DynamoPythonTests/PythonEvalTests.cs

@@ -195,5 +195,34 @@ class myobj:
                 Assert.AreEqual("Output could not be converted to a .NET value", exc.Message);
             }
         }
+
+        [Test]
+        public void NonListIterablesCanBeOutput()
+        {
+            var code = @"
+s = { 'hello' }
+fs = frozenset({ 'world' })
+d = { 'one': 1 }
+dk = d.keys()
+dv = d.values()
+di = d.items()
+
+OUT = s,fs,dk,dv,di
+";
+            var expected = new ArrayList
+            {
+                new ArrayList { "hello" },
+                new ArrayList { "world" },
+                new ArrayList { "one" },
+                new ArrayList { 1 },
+                new ArrayList { new ArrayList { "one", 1 } }
+            };
+            var empty = new ArrayList();
+            foreach (var pythonEvaluator in Evaluators)
+            {
+                var output = pythonEvaluator(code, empty, empty);
+                Assert.AreEqual(expected, output);
+            }
+        }
     }
 }