code: def return_type(rettype):
      
      def wrap(f):
          @functools.wraps(f)
          def converter(*pargs, **kwargs):
              # Run the function to capture the output.
              result = f(*pargs, **kwargs)
  
              # Convert the result using the return type function.
              try:
                  result = rettype(result)
              except ValueError as e:
                  http_status(500, "Return Value Conversion Failed")
                  content_type("application/json")
                  return {"error": str(e)}
              return result
  
          return converter
      return wrap
docs: Decorate a function to automatically convert its return type to a string
      using a custom function.
  
      Web-based service functions must return text to the client.  Tangelo
      contains default logic to convert many kinds of values into string, but this
      decorator allows the service writer to specify custom behavior falling
      outside of the default.  If the conversion fails, an appropriate server
      error will be raised.