namespace pythonnet_demo
{
    internal class MyClass
    {
        public object __repr__()
        {
            return "Test repr!";
        }

        public object __getattribute__(string name)
        {
            return "__getattribute__ works!";
        }

    }
}

using Python.Runtime;
using System.IO;

namespace pythonnet_demo
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string pythonHome = @"C:\dev\python";
            Runtime.PythonDLL = Path.Combine(pythonHome, "python310.dll");
            PythonEngine.PythonHome = pythonHome;
            PythonEngine.Initialize();

            MyClass obj = new MyClass();

            using (Py.GIL())
            {
                PyModule _scope = Py.CreateScope("__main__");
                _scope.Set("obj", obj);

                //Test repr, works as expected, "Test repr!" printed to console
                _scope.Exec("print(repr(obj))");

                //Test __getattribute__, throws exception, 'AttributeError', no attribute X
                _scope.Exec("print(obj.X)");
            }
        }
    }
}

class MyClassPy:
    def __repr__(self):
        return "Test repr!"
    def __getattribute__(self, name):
        return "__getattribute__ works!"

obj = MyClassPy()
print(repr(obj))
print(obj.X)

Test repr!
__getattribute__ works!