code: def get_plus_and_delete(self, prop):
          
          val = self.plus[prop]
          del self.plus[prop]
          return val
docs: get a copy of the property (parameter) in self.plus, delete the original and return the
          value of copy
  
          :param prop: a property
          :type prop: str
          :return: return the value of the property
          :rtype: str