coding=utf-8

import time
import threading
class Account:
def __init__(self, _id, balance, lock):

self.id = _id 
self.balance = balance 
self.lock = lock 

def withdraw(self, amount):

self.balance -= amount 

def deposit(self, amount):

self.balance += amount 

def transfer(_from, to, amount):
if _from.lock.acquire():#锁住自己的账户

_from.withdraw(amount) 
time.sleep(1)#让交易时间变长，2个交易线程时间上重叠，有足够时间来产生死锁 
print 'wait for lock...'
if to.lock.acquire():#锁住对方的账户 
  to.deposit(amount) 
  to.lock.release() 
_from.lock.release() 

print 'finish...'

a = Account('a',1000, threading.Lock())
b = Account('b',1000, threading.Lock())
threading.Thread(target = transfer, args = (a, b, 100)).start()
threading.Thread(target = transfer, args = (b, a, 200)).start()

当进程执行if语句里面lock.acquire()时会一直等待锁的释放吗，为什么lock.acquire()失败时不会跳过if执行后面的语句？