Исправление дека

class Dek:
def __init__(self, max_size):
    self._data = [None] * max_size
    self._front = max_size - 1
    self._back = 0
    self._size = 0

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

def push_back(self, value):
    self._back = self._push(self._back, 1, value)

def pop_back(self):
    self._back, value = self._pop(self._back, 1)
    return value

def push_front(self, value):
    self._front = self._push(self._front, -1, value)

def pop_front(self):
    self._front, value = self._pop(self._front, -1)
    return value

def _push(self, i, di, value):
    if self._size >= len(self._data):
        raise OverflowError
    self._data[i] = value
    self._size += 1
    return (i + di) % len(self._data)

def _pop(self, i, di):
    if self._size <= 0:
        raise IndexError
    j = (i - di) % len(self._data)
    x = self._data[j]
    self._data[j] = None
    self._size -= 1
    return j, x


def main():
    count_command = int(input())
    queue_size = int(input())

    queue = Dek(queue_size)
    for _ in range(count_command):
        verb, *values = input().split()
        op = getattr(queue, verb)
        values = tuple(map(int, values))
         try:
            result = op(*values)
        except (IndexError, OverflowError):
            result = 'error'
        if result is not None:
            print(result)


if __name__ == '__main__':
    main()

Нужна приватность для полей self._data = [None] * max_size пытаюсь использовать @property, но выдает ошибку inconsistent use of tabs and spaces in indentation
Как это исправить?