Manipulating index value, what is wrong with this code?

[Emun]

I want to manipulate an index value on list1, but can't figure out why the manipulation('alt') appears at two locations instead of just one. list2 shows correctly what I want to do on list1.

list1 = []
list2 = [[[40], 70], [[[40], 70], 90]]


def append_values():

    amount = None

    if len(list1) == 0:
        amount = 70
        list1.append([[40],amount])
    else:
        amount = 90
        list1.append([list1[-1],amount])
    


def alter_lists():

    print('ori: ', list1) #Orginal list
    list1[1][0][1] = "alt"
    print('alt: ', list1)   #Altered list

    print('\n')

    print('ori: ', list2) #Orginal list
    list2[1][0][1] = 'alt'
    print('alt: ', list2)  #Altered list


append_values()
append_values()
alter_lists()

Output:

ori:  [[[40], 70], [[[40], 70], 90]]
alt:  [[[40], 'alt'], [[[40], 'alt'], 90]]


ori:  [[[40], 70], [[[40], 70], 90]]
alt:  [[[40], 70], [[[40], 'alt'], 90]]