编程实现集合数据类型，完成并、交、差、对称差代码

以下是 Python 代码实现：

class Set:
    def __init__(self, items=[]):
        self.items = []
        for item in items:
            if item not in self.items:
                self.items.append(item)

    def __repr__(self):
        return f"Set({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 union(self, other_set):
        union_set = Set(self.items)
        for item in other_set.items:
            if item not in union_set.items:
                union_set.items.append(item)
        return union_set

    def intersect(self, other_set):
        intersect_set = Set()
        for item in self.items:
            if item in other_set.items:
                intersect_set.items.append(item)
        return intersect_set

    def difference(self, other_set):
        difference_set = Set(self.items)
        for item in other_set.items:
            if item in difference_set.items:
                difference_set.items.remove(item)
        return difference_set

    def symmetric_difference(self, other_set):
        symmetric_difference_set = Set()
        for item in self.items:
            if item not in other_set.items:
                symmetric_difference_set.items.append(item)
        for item in other_set.items:
            if item not in self.items:
                symmetric_difference_set.items.append(item)
        return symmetric_difference_set

其中，`Set` 类实现了集合数据类型，包括基本操作如 `add`、`remove`，以及集合并、交、差、对称差等操作。可以通过以下方式进行测试：

a = Set([1, 3, 5, 7])
b = Set([2, 4, 6, 7])

print(a.union(b))  # Set([1, 3, 5, 7, 2, 4, 6])
print(a.intersect(b))  # Set([7])
print(a.difference(b))  # Set([1, 3, 5])
print(a.symmetric_difference(b))  # Set([1, 3, 5, 2, 4, 6])