Buggy python submission (verdict: Time Limit Exceeded):

class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt

class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None

    def insert(self, num):
        new_elem = Node(num)

        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem

    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt

                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt

    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt

    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv

    def get_content(self):
        ret = []
        it = self.start

        while it is not None:
            ret.append(it.num)
            it = it.nxt

        return ' '.join(ret)

    def get_rcontent(self):
        ret = []
        it = self.last

        while it is not None:
            ret.append(it.num)
            it = it.prv

        return ' '.join(ret)

def _main():
    n = int(input())

    lst = DoublyLinkedList()
    
    for _ in range(n):
        cmd = input().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()

    print(lst.get_content())

if __name__ == '__main__':
    _main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Runtime Error):

class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt

class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None

    def insert(self, num):
        new_elem = Node(num)

        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem

    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt

                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt

    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt

    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv

    def get_content(self):
        ret = []
        it = self.start

        while it is not None:
            ret.append(it.num)
            it = it.nxt

        return ' '.join(ret)

    def get_rcontent(self):
        ret = []
        it = self.last

        while it is not None:
            ret.append(it.num)
            it = it.prv

        return ' '.join(ret)

def _main():
    n = int(input())

    lst = DoublyLinkedList()
    
    for _ in range(n):
        cmd = input().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()

    print(lst.get_content())

if __name__ == '__main__':
    _main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = ""
        node = self.start_node
        while node is not None:
            s += str(node.num) + " "
            node = node.next_node
        return s.strip()

def main():
    linked_list = LinkedList()
    c_num = int(sys.stdin.readline().strip())
    for i in range(0, c_num):
        line = sys.stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(int(line[1]))
        if op == "delete":
            linked_list.delete(int(line[1]))
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        a = []
        node = self.start_node
        while node is not None:
            a.append(str(node.num))
            node = node.next_node

        return ' '.join(a)

def main():
    linked_list = LinkedList()
    c_num = int(sys.stdin.readline().strip())
    for i in range(0, c_num):
        line = sys.stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(int(line[1]))
        if op == "delete":
            linked_list.delete(int(line[1]))
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = ""
        node = self.start_node
        while node is not None:
            s += node.num + " "
            node = node.next_node
        return s.strip()

def main():
    linked_list = LinkedList()
    c_num = int(sys.stdin.readline().strip())
    for i in range(0, c_num):
        line = sys.stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(line[1])
        if op == "delete":
            linked_list.delete(line[1])
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = []
        node = self.start_node
        while node is not None:
            s.append(node.num)
            node = node.next_node
        return ' '.join(s)

def main():
    linked_list = LinkedList()
    c_num = int(sys.stdin.readline().strip())
    for i in range(0, c_num):
        line = sys.stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(line[1])
        if op == "delete":
            linked_list.delete(line[1])
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = []
        node = self.start_node
        while node is not None:
            s.append(node.num)
            node = node.next_node
        return ' '.join(s)

def main():
    linked_list = LinkedList()
    c_num = int(stdin.readline().strip())
    for i in range(0, c_num):
        line = stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(line[1])
        if op == "delete":
            linked_list.delete(line[1])
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = ""
        node = self.start_node
        while node is not None:
            s += str(node.num) + " "
            node = node.next_node
        return s.strip()

def main():
    linked_list = LinkedList()
    c_num = int(stdin.readline().strip())
    for i in xrange(0, c_num):
        line = stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(int(line[1]))
        if op == "delete":
            linked_list.delete(int(line[1]))
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print str(linked_list)
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin

class Node:
    def __init__(self, num):
        self.prev = None
        self.next_node = None
        self.num = num
    def delete(self):
        if self.prev is not None:
            self.prev.next_node = self.next_node
        if self.next_node is not None:
            self.next_node.prev = self.prev

class LinkedList:
    def __init__(self):
        self.start_node = None
        self.last_node = None
    def add(self, num):
        node = Node(num)
        if self.start_node is None:
            self.start_node = node
            self.last_node = node
        elif self.last_node is None:
            self.last_node = self.start_node
            node.next_node = self.last_node
            self.last_node.prev = node
            self.start_node = node
        else:   
            self.start_node.prev = node
            node.next_node = self.start_node
            self.start_node = node
    def delete(self, num):
        node = self.start_node
        while node is not None:
            if node.num == num:
                if node == self.start_node:
                    self.delete_first()
                elif node == self.last_node:
                    self.delete_last()
                else:
                    node.delete()
                break
            node = node.next_node
    def delete_last(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.last_node
            self.last_node = self.last_node.prev
            node.delete()
    def delete_first(self):
        if self.start_node == self.last_node:
            self.start_node = None
            self.last_node = None
        else:
            node = self.start_node
            self.start_node = self.start_node.next_node
            node.delete()
    def __str__(self):
        s = ""
        node = self.start_node
        while node is not None:
            s += str(node.num) + " "
            node = node.next_node
        return s.strip()

def main():
    linked_list = LinkedList()
    c_num = int(stdin.readline().strip())
    for i in range(0, c_num):
        line = stdin.readline().strip().split(" ")
        op = line[0]
        if op == "insert":
            linked_list.add(int(line[1]))
        if op == "delete":
            linked_list.delete(int(line[1]))
        if op == "deleteFirst":
            linked_list.delete_first()
        if op == "deleteLast":
            linked_list.delete_last()
        #print linked_list
    print(str(linked_list))
    
if __name__ == "__main__":
    main()

Fixed submission:
class Node(object):
    def __init__(self, num, prv = None, nxt = None):
        self.num = num
        self.prv = prv
        self.nxt = nxt
 
 
class DoublyLinkedList(object):
    def __init__(self):
        self.start = self.last = None
 
    def insert(self, num):
        new_elem = Node(num)
 
        if self.start is None:
            self.start = self.last = new_elem
        else:
            new_elem.nxt = self.start
            self.start.prv = new_elem
            self.start = new_elem
 
    def delete_num(self, target):
        it = self.start
        while it is not None:
            if it.num == target:
                if it.prv is None and it.nxt is None:
                    self.start = self.last = None
                else:
                    if it.prv is not None:
                        it.prv.nxt = it.nxt
                    else:
                        self.start = self.start.nxt
 
                    if it.nxt is not None:
                        it.nxt.prv = it.prv
                    else:
                        self.last = self.last.prv
                break
            it = it.nxt
 
    def delete_start(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.start.nxt.prv = None
            self.start = self.start.nxt
 
    def delete_last(self):
        if self.start is self.last:
            self.start = self.last = None
        else:
            self.last.prv.nxt = None
            self.last = self.last.prv
 
    def get_content(self):
        ret = []
        it = self.start
 
        while it is not None:
            ret.append(it.num)
            it = it.nxt
 
        return ' '.join(ret)
 
 
def _main():
    from sys import stdin
 
    n = int(input())
 
    lst = DoublyLinkedList()
     
    for _ in range(n):
        cmd = stdin.readline().strip().split()
        if cmd[0] == 'insert':
            lst.insert(cmd[1])
        elif cmd[0] == 'delete':
            lst.delete_num(cmd[1])
        elif cmd[0] == 'deleteFirst':
            lst.delete_start()
        elif cmd[0] == 'deleteLast':
            lst.delete_last()
 
    print(lst.get_content())
 
 
if __name__ == '__main__':
    _main()