Environment

• Pythonnet version: 2.4.0.dev0 (master; #19d854c)
• Python version: 3.6.3 (v3.6.3:2c5fed8, Oct 3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
• Operating System: Windows 10 Pro 64 Bit (1803; 17134.5)

Details

• Describe what you were trying to get done.

1. Just call str python built-in function with C# class
2. Raise UnicodeDecodeError if value is 안녕
3. Return 안녕PADD if value is `안녕PADDINGX"

It seems like failure str convert with ToString() function only.
(Another method, nor read value does not problem)

• What commands did you run to trigger this issue? If you can provide a
  Minimal, Complete, and Verifiable example
  this will help us understand the issue.

namespace Hello
{
    public class World
    {
        public string value = "안녕";

        public string GetString()
        {
            return value;
        }

        public override string ToString()
        {
            return value;
        }
    }
}

import clr
clr.AddReference("hello")
from Hello import World
world = World()
print(1, str(world.value))
print(2, str(world.GetString()))
print(3, str(world))

• If there was a crash, please include the traceback here.

1 안녕
2 안녕
Traceback (most recent call last):
  File "main.py", line 7, in <module>
    str(hello)
UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 0-1: unexpected end of data