Merge sort in python

merge-sort.py

def merge_sort(ar, start, end): 
    qtd = end - start 
    if qtd > 1: 
        mid = int((start + end) / 2) 
        merge_sort(ar, start, mid) 
        merge_sort(ar, mid, end) 
        intercalate(ar, start, mid, end) 
    return ar
  
def intercalate(ar, start, mid, end): 
    sorted_ar = [] 
    i = start 
    j = mid 
    
    while i < mid  and j < end: 
        if ar[i] < ar[j]: 
            sorted_ar.append(ar[i]) 
            i += 1 
        else: 
            sorted_ar.append(ar[j]) 
            j += 1 
       
    while i < mid: 
        sorted_ar.append(ar[i]) 
        i += 1 
              
    while j < end: 
        sorted_ar.append(ar[j]) 
        j += 1 
              
    for i in range(0, len(sorted_ar)): 
        ar[start + i] = sorted_ar[i]
 

merge_sort([99, 206, -77, 2, 3, 6, 1, 4, 5, 8, 25], 0, 11)