Get the wrong sort of an array (writing heap sort in Python)

I have written the following heap sort code and I get the wrong output (not sorted) at times and I can't seem to find why...any help will be much appreciated! (WARNING: I am still learning Python that might be the problem)

def heap_sort(self, a):

    self.build_max_heap(a)
    n = len(a)-1
    i = len(a)-1

    for i in range(len(a)-1, 1):
        temp = a[0]
        a[0] = a[i]
        a[i] = temp
        a.heapsize = heapsize - 1
        self.max_heapify(a, 0)       #rebuild max heap at with new root



def max_heapify(self, a, i):

    left = (2*(i+1))-1      #left child of i
    right = 2*(i+1)             #right child of i
    largest = i

    if left < a.heapsize and a[left] > a[i]:
        largest = left

    if right < a.heapsize and a[right] > a[largest]:
        largest = right

    if largest != i:
        temp = a[largest]
        a[largest] = a[i]
        a[i] = temp
        self.max_heapify(a, largest)



def build_max_heap(self, a):

    heapsize = len(a)
    i = int(heapsize/2)-1

    for i in range(i, 0):
        self.max_heapify(a, i)

These are my tests:

#--Test for 0 in array--#
def zero_array(self):
    a = [12,0,232]
    print self.sort.heap_sort(a)
    return

#--Test for duplicate in array--#
def duplicate_array(self):
    a = [12, 12, 7]
    print self.sort.heap_sort(a)
    return

#--Test for all same values in array--#
def allsame_array(self):
    a = [1,1,1]
    print self.sort.heap_sort(a)
    return

#--Test for negative values in array--#
def negative_array(self):
    a = [-23, -2, 123]
    print self.sort.heap_sort(a)
    return

I get the following returned arrays (which are suppose to be sorted):

    [12, 0, 232]
    [12, 12, 7]
    [1, 1, 1]
    [-23, -2, 123]