编写一个python语言 实现字典模型

以下是一个简单的Python字典模型实现：

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

    def add(self, key, value):
        self._items[key] = value

    def remove(self, key):
        del self._items[key]

    def contains(self, key):
        return key in self._items

    def get(self, key):
        return self._items.get(key, None)

    def keys(self):
        return list(self._items.keys())

    def values(self):
        return list(self._items.values())

    def items(self):
        return list(self._items.items())

    def clear(self):
        self._items = {}

    def size(self):
        return len(self._items)

使用示例：

d = Dictionary()
d.add('apple', 1)
d.add('banana', 2)
d.add('cherry', 3)

print(d.contains('banana'))  # 输出 True
print(d.get('cherry'))  # 输出 3

d.remove('banana')
print(d.keys())  # 输出 ['apple', 'cherry']

print(d.items())  # 输出 [('apple', 1), ('cherry', 3)]

d.clear()
print(d.size())  # 输出 0
``