元祖的修改：
元祖的元素不可修改
a = (1,2,3,4)
del a[0]
>>>Traceback (most recent call last):
File "<pyshell#38>", line 1, in <module>
del a[0]
TypeError: 'tuple' object doesn't support item deletion
元祖的元素的元素可以修改
a = (1,2,3,{'a':'b'})
(a[3]['a'] = 'c')
print (a)
>>>(1,2,3,{'a':'c'})