python3线程安全要怎么实现？

import threading

def print_number():

    number = 42

    print(threading.current_thread().name, number)

t1 = threading.Thread(target=print_number)

t2 = threading.Thread(target=print_number)

t1.start()

t2.start()

import threading

number = 42

def print_number():

print(threading.current_thread().name, number)