code: def get_thunk_env(self, k):
      
      if k not in self.__items:
        raise exceptions.EvaluationError('Unknown key: %r in tuple %r' % (k, self))
      x = self.__items[k]
  
      env = self.env(self)
  
      # Bind this to the tuple's parent environment
      if isinstance(x, framework.BindableThunk):
        return x.bind(self.__parent_env), env
      return x, env
docs: Return the thunk AND environment for validating it in for the given key.
  
      There might be different envs in case the thunk comes from a different (composed) tuple. If the thunk needs its
      environment bound on retrieval, that will be done here.