class Node(object):
 
    def __init__(self, data, next):
        self.data = data
        self.next = next
 
 
class SingleList(object):
 
    head = None
    tail = None
 
    def show(self):
        print "Showing list data:"
        current_node = self.head
        while current_node is not None:
            print current_node.data, " -> ",
            current_node = current_node.next
        print None
 
    def append(self, data):
        node = Node(data, None)
        if self.head is None:
            self.head = self.tail = node
        else:
            self.tail.next = node
        self.tail = node
 
    def remove(self, node_value):
        current_node = self.head
        previous_node = None
        while current_node is not None:
            if current_node.data == node_value:
                # if this is the first node (head)
                if previous_node is not None:
                    previous_node.next = current_node.next
                else:
                    self.head = current_node.next
 
            # needed for the next iteration
            previous_node = current_node
            current_node = current_node.next
 
 
s = SingleList()
s.append(31)
s.append(2)
s.append(3)
s.append(4)
 
s.show()
s.remove(31)
s.remove(3)
s.remove(2)
s.show()

class Node(object):
 
    def __init__(self, data, prev, next):
        self.data = data
        self.prev = prev
        self.next = next
 
 
class DoubleList(object):
 
    head = None
    tail = None
 
    def append(self, data):
        new_node = Node(data, None, None)
        if self.head is None:
            self.head = self.tail = new_node
        else:
            new_node.prev = self.tail
            new_node.next = None
            self.tail.next = new_node
            self.tail = new_node
 
    def remove(self, node_value):
        current_node = self.head
 
        while current_node is not None:
            if current_node.data == node_value:
                # if it's not the first element
                if current_node.prev is not None:
                    current_node.prev.next = current_node.next
                    current_node.next.prev = current_node.prev
                else:
                    # otherwise we have no prev (it's None), head is the next one, and prev becomes None
                    self.head = current_node.next
                    current_node.next.prev = None
 
            current_node = current_node.next
 
    def show(self):
        print "Show list data:"
        current_node = self.head
        while current_node is not None:
            print current_node.prev.data if hasattr(current_node.prev, "data") else None,
            print current_node.data,
            print current_node.next.data if hasattr(current_node.next, "data") else None
 
            current_node = current_node.next
        print "*"*50
 
 
d = DoubleList()
 
d.append(5)
d.append(6)
d.append(50)
d.append(30)
 
d.show()
 
d.remove(50)
d.remove(5)
 
d.show()