用于返回字典的Python类

class Dictionary:
    def __init__(self):
        self.dict = {}

    def add_item(self, key, value):
        self.dict[key] = value

    def remove_item(self, key):
        if key in self.dict:
            del self.dict[key]

    def update_item(self, key, value):
        if key in self.dict:
            self.dict[key] = value

    def get_item(self, key):
        if key in self.dict:
            return self.dict[key]
        else:
            return None

    def get_all_items(self):
        return self.dict