关于函数修改列表的相关问题

代码如下：
# -*-coding:gb2312 -*-
def show_magicians(magicians):
    print("\nthe magicians are:")
    for magician in magicians:
        mag = magician.title()
        print(mag)
        
def make_great(magicians):
    for magician in magicians:
        magician = "The great" + magician.title()
        print(magician)
magicians=['arthur','may','leo']
copy = magicians[:]
show_magicians(magicians)
make_great(copy)
print(copy)

按照我的理解，当调用了make_great()函数后，copy列表应该已经修改了，但是为什么打印出的结果，copy列表还是['arthur','may','leo']？
新人，求大神指教！！！！