C# enums to work as proper enums in Python

src/embed_tests/TestMethodBinder.cs

@@ -815,6 +815,20 @@ public string VariableArgumentsMethod(params PyObject[] paramsParams)
                 return "VariableArgumentsMethod(PyObject[])";
             }
 
+            // ----
+
+            public string MethodWithEnumParam(SomeEnu enumValue, string symbol)
+            {
+                return $"MethodWithEnumParam With Enum";
+            }
+
+            public string MethodWithEnumParam(PyObject pyObject, string symbol)
+            {
+                return $"MethodWithEnumParam With PyObject";
+            }
+
+            // ----
+
             public string ConstructorMessage { get; set; }
 
             public OverloadsTestClass(params CSharpModel[] paramsParams)
@@ -1117,6 +1131,26 @@ def get_instance():
             Assert.AreEqual("OverloadsTestClass(PyObject[])", instance.GetAttr("ConstructorMessage").As<string>());
         }
 
+        [Test]
+        public void EnumHasPrecedenceOverPyObject()
+        {
+            using var _ = Py.GIL();
+
+            var module = PyModule.FromString("EnumHasPrecedenceOverPyObject", @$"
+from clr import AddReference
+AddReference(""System"")
+from Python.EmbeddingTest import *
+
+class PythonModel(TestMethodBinder.CSharpModel):
+    pass
+
+def call_method():
+    return TestMethodBinder.OverloadsTestClass().MethodWithEnumParam(TestMethodBinder.SomeEnu.A, ""Some string"")
+");
+
+            var result = module.GetAttr("call_method").Invoke();
+            Assert.AreEqual("MethodWithEnumParam With Enum", result.As<string>());
+        }
 
         // Used to test that we match this function with Py DateTime & Date Objects
         public static int GetMonth(DateTime test)

src/perf_tests/Python.PerformanceTests.csproj

@@ -13,7 +13,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.*" />
-    <PackageReference Include="quantconnect.pythonnet" Version="2.0.44" GeneratePathProperty="true">
+    <PackageReference Include="quantconnect.pythonnet" Version="2.0.45" GeneratePathProperty="true">
       <IncludeAssets>compile</IncludeAssets>
     </PackageReference>
   </ItemGroup>
@@ -25,7 +25,7 @@
   </Target>
 
   <Target Name="CopyBaseline" AfterTargets="Build">
-    <Copy SourceFiles="$(NuGetPackageRoot)quantconnect.pythonnet\2.0.44\lib\net9.0\Python.Runtime.dll" DestinationFolder="$(OutDir)baseline" />
+    <Copy SourceFiles="$(NuGetPackageRoot)quantconnect.pythonnet\2.0.45\lib\net9.0\Python.Runtime.dll" DestinationFolder="$(OutDir)baseline" />
   </Target>
 
   <Target Name="CopyNewBuild" AfterTargets="Build">

src/runtime/Converter.cs

@@ -18,6 +18,13 @@ namespace Python.Runtime
     [SuppressUnmanagedCodeSecurity]
     internal class Converter
     {
+        /// <summary>
+        /// We use a cache of the enum values references so that we treat them as singletons in Python.
+        /// We just try to mimic Python enums behavior, since Python enum values are singletons,
+        /// so the `is` identity comparison operator works for C# enums as well.
+        /// </summary>
+
+        private static readonly Dictionary<object, PyObject> _enumCache = new();
         private Converter()
         {
         }
@@ -226,6 +233,16 @@ internal static NewReference ToPython(object? value, Type type)
                 return resultlist.NewReferenceOrNull();
             }
 
+            if (type.IsEnum)
+            {
+                if (!_enumCache.TryGetValue(value, out var cachedValue))
+                {
+                    _enumCache[value] = cachedValue = CLRObject.GetReference(value, type).MoveToPyObject();
+                }
+
+                return cachedValue.NewReferenceOrNull();
+            }
+
             // it the type is a python subclass of a managed type then return the
             // underlying python object rather than construct a new wrapper object.
             var pyderived = value as IPythonDerivedType;

src/runtime/MethodBinder.cs

@@ -383,6 +383,17 @@ internal static int ArgPrecedence(Type t, bool isOperatorMethod)
                 return 3000;
             }
 
+            if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>))
+            {
+                // Nullable<T> is a special case, we treat it as the underlying type
+                return ArgPrecedence(Nullable.GetUnderlyingType(t), isOperatorMethod);
+            }
+
+            if (t.IsEnum)
+            {
+                return -2;
+            }
+
             if (t.IsAssignableFrom(typeof(PyObject)) && !isOperatorMethod)
             {
                 return -1;

src/runtime/Properties/AssemblyInfo.cs

@@ -4,5 +4,5 @@
 [assembly: InternalsVisibleTo("Python.EmbeddingTest, PublicKey=00240000048000009400000006020000002400005253413100040000110000005ffd8f49fb44ab0641b3fd8d55e749f716e6dd901032295db641eb98ee46063cbe0d4a1d121ef0bc2af95f8a7438d7a80a3531316e6b75c2dae92fb05a99f03bf7e0c03980e1c3cfb74ba690aca2f3339ef329313bcc5dccced125a4ffdc4531dcef914602cd5878dc5fbb4d4c73ddfbc133f840231343e013762884d6143189")]
 [assembly: InternalsVisibleTo("Python.Test, PublicKey=00240000048000009400000006020000002400005253413100040000110000005ffd8f49fb44ab0641b3fd8d55e749f716e6dd901032295db641eb98ee46063cbe0d4a1d121ef0bc2af95f8a7438d7a80a3531316e6b75c2dae92fb05a99f03bf7e0c03980e1c3cfb74ba690aca2f3339ef329313bcc5dccced125a4ffdc4531dcef914602cd5878dc5fbb4d4c73ddfbc133f840231343e013762884d6143189")]
 
-[assembly: AssemblyVersion("2.0.44")]
-[assembly: AssemblyFileVersion("2.0.44")]
+[assembly: AssemblyVersion("2.0.45")]
+[assembly: AssemblyFileVersion("2.0.45")]

src/runtime/Python.Runtime.csproj

@@ -5,7 +5,7 @@
     <RootNamespace>Python.Runtime</RootNamespace>
     <AssemblyName>Python.Runtime</AssemblyName>
     <PackageId>QuantConnect.pythonnet</PackageId>
-    <Version>2.0.44</Version>
+    <Version>2.0.45</Version>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <RepositoryUrl>https://github.com/pythonnet/pythonnet</RepositoryUrl>