[C++-sig] boost::python: wrap std::string?

[paul.bridger]

Okay, hopefully someone can tell me what I'm doing wrong here.
I am trying to wrap a class that derives from std::string. Everything seems 
to go just fine until I try to import the derived class in Python. This is 
the error message I get:

RuntimeError: extension class wrapper for base class class 
std::basic_string<char,struct std::char_traits<char>,class 
std::allocator<char> > has not been created yet

What is my best course of action?