Run time error in python while implementing merge sort

#1

def merge(lh,rh):
al = [0] * (len(lh) + len(rh))
i = 0
j = 0
k = 0

while i < len(lh) and j < len(rh):
    if(lh[i] <= rh[j]):
        al[k] = lh[i]
        i+=1
        k+=1
    else:
        al[k] = rh[j]
        j+=1
        k+=1

while i < len(lh):
    al[k] = lh[i]
    i+=1
    k+=1

while j < len(rh):
    al[k] = rh[j]
    j+=1
    k+=1

return al

def mergeSort(arr,l,r):
if(l == r):
nl = [arr[l]]
return nl

mid = int((l + r)/2);

lh = mergeSort(arr,l,mid)
rh = mergeSort(arr,mid+1,r)

ans = merge(lh,rh)
return ans

n = int(input())
str = input().split(" ")
list = [int(no) for no in str]
list = mergeSort(list,0,len(list) - 1)

for i in list:
print(i,end = " ")

Here is my code it passes all of my custom test cases but gives run time error after submission