using System;
using Python.Runtime;

namespace MyNamespace
{
    public static class MyClass
    {
        public static void TestInt(int i)
        {
            Console.WriteLine(i);
        }

        public static void TestDateTime(DateTime dateTime)
        {
            Console.WriteLine(dateTime);
        }
    }

    public class MyCodecs : IPyObjectDecoder
    {
        public static void Setup()
        {
            Console.WriteLine("Setup Called");
            PyObjectConversions.RegisterDecoder(new MyCodecs());
        }

        public bool CanDecode(PyObject objectType, Type targetType)
        {
            Console.WriteLine("CanDecode Called");
            return targetType == typeof(DateTime);
        }

        public bool TryDecode<T>(PyObject pyObj, out T value)
        {
            Console.WriteLine("TryDecode Called");
            var dt = new DateTime(
                pyObj.GetAttr("year").As<int>(),
                pyObj.GetAttr("month").As<int>(),
                pyObj.GetAttr("day").As<int>(),
                pyObj.GetAttr("hour").As<int>(),
                pyObj.GetAttr("minute").As<int>(),
                pyObj.GetAttr("second").As<int>());
            value = (T)(object)dt;
            return true;
        }
    }
}

import clr
from datetime import datetime
clr.AddReference('MyLibrary')


from MyNamespace import MyClass, MyCodecs

#these two work
MyCodecs.Setup()
MyClass.TestInt(22)

#error here
MyClass.TestDateTime(datetime(2021, 1, 22))

TypeError: No method matches given arguments for TestDateTime: (<class 'datetime.datetime'>)