Дек неограниченного размера

size = 0 
deque = []
queue_head = 0
queue_tail = 0 
 
def isempty():
    return len(deque) == 0
 
def push_back(val):
    global deque, size
    deque.append(val)
    size += 1
    print('ok')
 
 
def push_front(val):
    global deque, size
    deque.insert(0, val)
    size += 1
    print('ok')
 
 
def pop_front():
  global queue_head, size
  if not isempty():
    queue_head = deque[0]
    size -= 1
    return queue_head
  else:
    return 'error'
 
def pop_back():
  global queue_tail, size
  if not isempty():
    queue_tail = deque[-1]
    size -= 1
    return queue_tail
  else:
    return 'error'
 
def front():
  if not isempty(): 
    return deque[0]
  else:
    print('error')
 
def back():
  if not isempty(): 
    return deque[-1]
  else:
    print('error')
 
def clear():
  global deque
  deque[:] = []
  print('ok')
 
while True:
  s = input().split(' ')
  if s[0] == 'push_front':
    push_front(int(s[1]))
  elif s[0] == 'push_back':
    push_back(int(s[1]))
  elif s[0] == 'pop_back':
    print(pop_back())
  elif s[0] == 'pop_front':
    print(pop_front())
  elif s[0] == 'front':
    print(front())
  elif s[0] == 'back':
    print(back())
  elif s[0] == 'size':
    print(size)
  elif s[0] == 'clear':
    clear()
  elif s[0] == 'exit':
    print('bye')
    break

from collections import deque
 
d = deque()
n = str(input()).split()
 
 
def push_back(elem):
    d.append(elem)
    print("ok")
 
 
def push_front(elem):
    d.appendleft(elem)
    print("ok")
 
 
def pop_front():
    print(d.popleft())
 
 
def pop_back():
    print(d.pop())
 
 
def back():
    print(d[-1])
 
 
def front():
    print(d[0])
 
 
def size():
    print(len(d))
 
 
def clear():
    d.clear()
    print("ok")
 
 
def exit():
    print("bye")
 
 
while n[0] != 'exit':
    if n[0] == 'push_back':
        push_back(n[1])
    elif n[0] == 'push_front':
        push_front(n[1])
    elif n[0] == 'pop_back':
        if len(d) > 0:
            pop_back()
        else:
            print('error')
    elif n[0] == 'pop_front':
        if len(d) > 0:
            pop_front()
        else:
            print('error')
    elif n[0] == 'back':
        if len(d) > 0:
            back()
        else:
            print('error')
    elif n[0] == 'front':
        if len(d) > 0:
            front()
        else:
            print('error')
    elif n[0] == 'size':
        size()
    elif n[0] == 'clear':
        clear()
    n = str(input()).split()
exit()

class Deque:
    def __init__(self, *content: any):
        self.content: [any] = list(content)
 
    def push_front(self, element: any) -> str:
        self.content.insert(0, element)
        return "ok"
 
    def push_back(self, element: any) -> str:
        self.content.append(element)
        return "ok"
 
    def pop_front(self) -> any:
        return self.content.pop(0) if self.content else "error"
 
    def pop_back(self) -> any:
        return self.content.pop(-1) if self.content else "error"
 
    def front(self) -> any:
        return self.content[0] if self.content else "error"
 
    def back(self) -> any:
        return self.content[-1] if self.content else "error"
 
    def size(self) -> int:
        return len(self.content)
 
    def clear(self):
        self.content.clear()
        return "ok"
 
 
deq = Deque()
for line in iter(input, "exit"):
    name, *args = line.split()
    print(getattr(deq, name)(*args))
print("bye")