python代码没有输出

请问以下代码为什么编译通过了，但是没有输出

current_users=["Amy","Tom","Jack","小明","小红"]
new_users=["Jack","A","B","C","Tom"]
for new_user in new_users:
    a=0
    for current_user in current_users:
        if new_user.lower()==current_user.lower():
            a==1
    if a==1:
        print(new_user+" has been used.")

第7行

==  改成 =

你这错误这么基础，一个=是赋值，两个=是比较