By default any public .NET type is visible to Python. If you want to hide .NET type from Python (for example because its conflicts with an existing Python type), you can mark it with with [PyExport(false)] attribute:

[Python.Runtime.PyExport(false)]
public class IamInvisibleToPython
{
  ...
}

You can hide your entire assembly by applying that attribute to it:

[assembly: Python.Runtime.PyExport(false)]