code: def serialize(self):
          
          return {'operand': self.operand, 'sons': [serialize(elem) for elem in self.sons],
                  'of_values': self.of_values, 'is_of_mul': self.is_of_mul,
                  'not_value': self.not_value}
docs: This function serialize into a simple dict object.
          It is used when transferring data to other daemons over the network (http)
  
          Here we directly return all attributes
  
          :return: json representation of a DependencyNode
          :rtype: dict