code: def behavior(f):
      
      @wraps(f)
      def wrapper(*args):
          message = args[-1]
          if isinstance(message, MutableMapping):
              message = Message(message)
          f(*(args[:-1] + (message,)))
      return wrapper
docs: Decorator for declaring a function as behavior.
  
      Use as::
  
          @behavior
          def fun(x, y, self, msg):
              ...
  
      And create or become this behavior by passing the two arguments
      `x` and `y`.