QUICK SORT IN PYTHON LANGUAGE CODE

def quickSort(alist): 
   quickSortHelper(alist,0,len(alist)-1) 

def quickSortHelper(alist,first,last): 
   if first<last: 

       splitpoint = partition(alist,first,last) 

       quickSortHelper(alist,first,splitpoint-1) 
       quickSortHelper(alist,splitpoint+1,last) 


def partition(alist,first,last): 
   pivotvalue = alist[first] 

   leftmark = first+1 
   rightmark = last 

   done = False 
   while not done: 

       while leftmark <= rightmark and \ 
               alist[leftmark] <= pivotvalue: 
           leftmark = leftmark + 1 

       while alist[rightmark] >= pivotvalue and \ 
               rightmark >= leftmark: 
           rightmark = rightmark -1 

       if rightmark < leftmark: 
           done = True 
       else: 
           temp = alist[leftmark] 
           alist[leftmark] = alist[rightmark] 
           alist[rightmark] = temp 

   temp = alist[first] 
   alist[first] = alist[rightmark] 
   alist[rightmark] = temp 


   return rightmark 

alist = [54,26,93,17,77,31,44,55,20] 
quickSort(alist) 
print(alist)