class Link:
    class Node:
        def __init__(self, item, next=None):
            self.item = item
            self.next = next

    class LinkListIterator:
        def __init__(self, node):
            self.node = node

        def __next__(self):
            if self.node:
                cur_node = self.node
                self.node = self.node.next
                return cur_node.item
            else:
                raise StopIteration

        def __iter__(self):
            pass

    def __init__(self, iterable=None):
        self.head = None
        self.tail = None
        self.size = 0
        if iterable:
            self.extend(iterable)

    def ins_head(self, item):
        new_node = Link.Node(item, None)
        if self.size == 0:
            self.tail = new_node
        else:
            new_node.next = self.head
        self.head = new_node
        self.size += 1

    def ins_tail(self, item):
        new_node = Link.Node(item, None)
        if self.size == 0:
            self.head = new_node
        else:
            self.tail.next = new_node
        self.tail = new_node
        self.size += 1

    def print_link(self):
        for i in self:
            print(i, end=' ')
        print()

    def del_head(self):
        if self.size > 0:
            temp = self.head
            self.head = self.head.next
            self.size -= 1
            return temp
        else:
            raise IndexError

    def del_item(self, item):
        if self.size > 0:
            cur_node = self.head
            for i in range(self.size):
                if cur_node.next and cur_node.next.item == item:
                    temp = cur_node.next
                    cur_node.next = cur_node.next.next
                    self.size -= 1
                    return temp.item
                cur_node = cur_node.next
            else:
                print('找不到要刪除的元素')
                return None
        else:
            raise IndexError

    def find(self, item):
        for i in self:
            if i == item:
                return True
        else:
            return False

    def extend(self, iterable):
        for i in iterable:
            self.ins_tail(i)

    def __iter__(self):
        return self.LinkListIterator(self.head)

    def __str__(self):
        return '<<' + ','.join(map(str, self)) + '>>'

    __repr__ = __str__


if __name__ == '__main__':
    link = Link(['a', 'b', 'c'])
    link.ins_head(1)
    link.ins_head(2)
    link.ins_head(3)
    link.print_link()
    link.ins_tail(4)
    link.ins_tail(5)
    link.ins_tail(6)
    link.print_link()
    print('-------------')
    print('--', link.del_item(5))
    print(link)