Creating custom sqlalchemy types

I am trying to save ipaddress in a table. Created a custom type as follows:

class MCastIP(sqlalchemy.types.TypeDecorator):
  impl = sqlalchemy.types.Integer
  def process_bind_param(self, value, dialect):
    return int(IPAddress(value))
  def process_result_value(self, value, dialect):
    return IPAddress(value)

This seem to work fine but just wondering if I have to implement any other function to be complete. Eg: python_type. Is the following needed? When will this be called and how do I call explicitly and test it works?

def python_type(self):
   return IPAddress