class Node:
    def __init__(self, data=None, prev=None, next=None):
        self.data = data
        self.prev = prev
        self.next = next

class DLL:

    def __init__(self):
        self.header = Node()
        self.trailer = Node()
        self.header.next = self.trailer
        self.trailer.prev = self.header
        self.current = self.header
        self.size = 0

    def __str__(self):
        print_str = ''
        value = self.current
        while value != None:
            print_str += str(value.data) + ' '
            value = value.next
        return print_str

    def __len__(self):
        return self.size

    def is_empty(self):
        return self.size == 0

    def insert(self, value):
        new_node = Node(value)
        if self.current == self.header:
            self.current = self.current.next
        new_node.prev = self.current.prev
        new_node.next = self.current
        self.current.prev = new_node
        self.current = new_node

        self.size += 1
        return self.current

    def remove(self):
        if self.is_empty():
            return None
        else:
            self.current.next = self.current
            self.current.prev = None

        self.size -= 1

    def get_value(self):
        if self.is_empty():
            return None
        return self.current.data

    def move_to_next(self):
        if self.current == self.trailer:
            return None
        else:
            self.current = self.current.next
        return self.current

    def move_to_prev(self):
        if self.current == self.header:
            return None
        else:
            self.current = self.current.prev
        return self.current

    def move_to_pos(self, position):
        if self.current == self.header == self.trailer:
            return None

    def remove_all(self, value):
        self.size = 0
        self.header = self.current
        return self.size

    def reverse(self):
        pass

    def sort():
        pass