import threading

class BankAccount(object):

def __init__(self):

self.is_open = False

self.balance = 0

self.lock = threading.Lock()

def get_balance(self):

with self.lock:

if self.is_open:

return self.balance

else:

raise ValueError

def open(self):

self.is_open = True

def deposit(self, amount):

with self.lock:

if self.is_open and amount > 0:

self.balance += amount

else:

raise ValueError

def withdraw(self, amount):

with self.lock:

if self.is_open and 0 < amount <= self.balance:

self.balance -= amount

else:

raise ValueError

def close(self):

self.is_open = False