理解python函数传参机制

num=10
string='test'
tupleset=(1,2,3)
listset=[9,8,7]
def change(num,string,tupleset,listset):
num+=1
string+=' into new words!'
#tupleset.add(12)   error
tupleset=(12,3,4,4)
listset.append(10000)
change(num,string,tupleset,listset)
print num,string,tupleset,listset