code: def move_items(self, from_group, to_group):
          
          if from_group not in self.keys() or len(self.groups[from_group]) == 0:
              return
  
          self.groups.setdefault(to_group, list()).extend(self.groups.get
                                                          (from_group, list()))
          if from_group in self.groups:
              del self.groups[from_group]
docs: Take all elements from the from_group and add it to the to_group.