Gotchas: when implementing delete() you need to handle in their own way head, tails and middle nodes.

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


class LinkedList(object):
    head = None
    tail = None

    def push(self, value):
        new_node = Node(value)
        
        if self.head is None:
            self.head = self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = new_node
            self.head = new_node


    def append(self, value):
        new_node = Node(value)

        if self.tail is None:
            self.tail = self.head = new_node
        else:
            new_node.prev = self.tail
            self.tail.next = new_node
            self.tail = new_node


    def delete(self, value):
        n = self.head

        # first node
        if n.value == value:
            if n.next is None and n.prev is None:
                self.head = self.tail = None
                print 'list is empty'
                return
            else:
                self.head = self.head.next
                self.head.prev = None
                return

        # middle nodes
        while n.next is not None:
            if n.value == value:
                n.prev.next = n.next
                n.next.prev = n.prev
                return
            n = n.next

        # last node
        if n.value == value:
            n.prev.next = None


    def show(self):
        n = self.head
        while n is not None:
            print n.value,
            n = n.next
        print

        
    def showBack(self):
        n = self.tail
        while n is not None:
            print n.value,
            n = n.prev
        print


l = LinkedList()
l.append(20)
l.append(30)
l.push(10)
l.show()
l.showBack()
l.delete(20)
l.show()
l.delete(10)
l.show()
l.delete(30)
l.show()

I personally like delete() implementation better:

def delete(self, value):      
    # delete head
    if self.head.value == value:
        # if head is the last node
        if self.head.next is None:
            self.head = self.tail = None
        else:
            self.head = self.head.next
            self.head.prev = None

    # delete tail
    elif self.tail.value == value:
        self.tail = self.tail.prev
        self.tail.next = None

    # delete middle nodes 
    else:
        n = self.head
        while n.value != value:
            n = n.next
        n.prev.next = n.next
        n.next.prev = n.prev