python多线程安全local()

import time
import threading
from threading import local

class Foo(local):
    pass
# 实例化(创建)对象
foo = Foo()
# 给Foo类添加静态变量
def add(i):
    foo.num = i
    time.sleep(1)
    # threading.current_thread().ident 线程PID
    print(foo.num, i, threading.current_thread().ident)


for i in range(20):
    # 开启多线程
    th = threading.Thread(target=add, args=(i,))
    th.start()