Python中如何实现享元模式？

class TreeType:
    def __init__(self, name, color):
        self.name = name
        self.color = color

    def __str__(self):
        return f'{self.color} {self.name}'

class Tree:
    def __init__(self, x, y, tree_type):
        self.x = x
        self.y = y
        self.tree_type = tree_type

    def __str__(self):
        return f'Tree at ({self.x}, {self.y}): {self.tree_type}'

class TreeFactory:
    def __init__(self):
        self.tree_types = {}

    def get_tree_type(self, name, color):
        key = f'{name}-{color}'
        if key not in self.tree_types:
            self.tree_types[key] = TreeType(name, color)
        return self.tree_types[key]

# 使用示例
factory = TreeFactory()

tree_type1 = factory.get_tree_type('Oak', 'Green')
tree_type2 = factory.get_tree_type('Pine', 'Brown')

tree1 = Tree(1, 2, tree_type1)
tree2 = Tree(3, 4, tree_type2)
tree3 = Tree(5, 6, tree_type1)

print(tree1)
print(tree2)
print(tree3)