comprehension syntax 有俩种list, dict
conditional expression:
if 在for后面, if修饰整个语句
never_login_users = [user for user in new_shared_user_ids if is_user_never_login(user)]
ternary operator:
if 在 for前面, 只修饰 最前面的user
never_login_users = [user if is_user_never_login(user) else '' for user in new_shared_user_ids]
