heap sort naive implementation

Question

I have some trouble with the sort function in the code
it doesn't give out the sorted array like i wanted.
anybody, help.
here's the code:
def sift_down(unsorted, index, size):
l = 2 * index +1
r = 2 * index +2
largest = index

# comparing a node an its left child
# size have to be minused 1 since we start at index 0
if l <= size-1 and unsorted[l] > unsorted[largest]:
largest = l
# comparing either the siblings or the node and its right child
if r <= size-1 and unsorted[r] > unsorted[largest]:
largest = r

if largest != index:
unsorted[index],unsorted[largest] = unsorted[largest],unsorted[index]
sift_down(unsorted, largest, size)

def build_heap(unsorted):
size = len(unsorted)
# we divide size by 2(to get to the leftmost part of the tree or heap) then minus 1 becoz we have to get to the almost last layer of the tree ->to work with the sub-tree
for i in range(size//2-1, -1, -1):
sift_down(unsorted, i, size)

def sort(unsorted):
size = len(unsorted)
build_heap(unsorted)
# size - 1 as we start at index 0
for i in range(size-1):
unsorted[0], unsorted[-1] = unsorted[-1], unsorted[0]
size -= 1
sift_down(unsorted, 0, size)
print(unsorted)

test = [7,6,8,9]
test2 = [1,3,7,4,5,6,2]
sort(test) # output: [7,9,8,6]

Answer 1

I'd recommend you to put your code in Sololearn Codeplayground so we could check it in interpreter.
At first glance I can say i do not see any variable passing between your main routine and subroutines. i. e. your 'largest' variable is not visible outside the subroutine scope.

Answer 2

here's the code in action:https://code.sololearn.com/ce579xBhfIz2/#py
and can you make it clear about you did not see 'that largest' variable is not visible outside the subroutine scope. thank you