锁

#多个线程操作同一个数据的时候，就得加锁
import  threading
num = 0
lock = threading.Lock()#申请一把锁
def add():
   global num
   lock.acquire()#加锁
   num+=1
   lock.release()#解锁
for i in range(20):
   t = threading.Thread(target=add,)
   t.start()

while threading.activeCount()!=1:
   pass
print(num)