python全局变量的修改 线程共享全局变量

箭头指向不变，而修改里面的值，则可不加global

如果箭头指向的方向变，则必须加global

至于哪些可变哪些不可变，要看具体的数据类型 数字，字符串、元组不可变，其它可变

num = 100

def test():
    global num
    num += 100

print(num)
test()
print(num)

 

 

import threading
import time

g_num = 100

def test1():
    global g_num
    g_num += 11
    print("---------test1--- g_num =%d----" % g_num)


def test2():
    print("---------test2--- g_num =%d----" % g_num)


def main():
    t1 = threading.Thread(target=test1)
    t2 = threading.Thread(target=test2)

    t1.start()
    time.sleep(1)

    t2.start()
    time.sleep(1)


    print("----in main Thread g_num = %d" % g_num)

if __name__ == "__main__":
    main()