python 编写一个类，实现添加元素（如果存在则不添加），删除元素，弹出元素（pop）,集合差集运算，集合并集运算，判断两个集合是否相等，>=运算符重载（集合包含关系），支持内置函数len，清空集合所有元素

下面是一个示例代码，实现了上述功能：

class MySet:
    def __init__(self):
        self.items = []

    def add(self, item):
        if item not in self.items:
            self.items.append(item)

    def remove(self, item):
        if item in self.items:
            self.items.remove(item)

    def pop(self):
        if len(self.items) == 0:
            return None
        return self.items.pop()

    def difference(self, other_set):
        result = MySet()
        for item in self.items:
            if item not in other_set.items:
                result.add(item)
        return result

    def union(self, other_set):
        result = MySet()
        for item in self.items:
            result.add(item)
        for item in other_set.items:
            result.add(item)
        return result

    def __eq__(self, other_set):
        if len(self.items) != len(other_set.items):
            return False
        for item in self.items:
            if item not in other_set.items:
                return False
        return True

    def __ge__(self, other_set):
        for item in other_set.items:
            if item not in self.items:
                return False
        return True

    def __len__(self):
        return len(self.items)

    def clear(self):
        self.items = []

使用示例：

set1 = MySet()
set1.add(1)
set1.add(2)
set1.add(3)

set2 = MySet()
set2.add(2)
set2.add(3)
set2.add(4)

set3 = set1.union(set2)
print(set3.items) # [1, 2, 3, 4]

set4 = set1.difference(set2)
print(set4.items) # [1]

print(set1 >= set4) # True

set1.clear()
print(len(set1.items)) # 0