Modified random quick sort - returning none

Question

I have an assignment in writing a modified quick sort. I know that the partition2 function is correct so the error must come from somewhere else (I think...).

I am getting "none" for any list I input; any help would be much appreciated!

Here is the code:

import numpy.random as rand

def randPartition(A,p,r): 
    randIndex =   rand.randint(p,r+1)   
    (A[randIndex],A[r])=(A[r],A[randIndex])  
    return partition2(A,p,r)

def partition2(A,p,r):
    x = A[r]
    i1 = p-1
    i2 = p-1
    for j in range(p,r):
        if A[j]==x:
            i2+=1
            (A[i2],A[j])=(A[j],A[i2])
        elif A[j]<x:
            i1+=1
            i2+=1
            (A[i1],A[j])=(A[j],A[i1])
    i2+=1
    (A[i2],A[r])=(A[r],A[i2])
    return (i1+1,i2)

def randQuickSort2(A): 
    def randQuickSortRec(A,p,r):
        if p<r: 
            q = randPartition(A,p,r)
            randQuickSortRec(A,p,q[0]-1)
            randQuickSortRec(A,q[1]+1,r) 
    randQuickSortRec(A,0,len(A)-1)


A3=[0,1,2,0,1,2,0,1,2,1]
A4=[5,6,5,5,1,3,5,2,1,7,9,5,15,100,5, 2,17,5,56]
print(randQuickSort2(A3))
print(randQuickSort2(A4))  

Answer 1

Your code is modifying the list in-place. The methods don't return anything - that's why you get None

Try printing the list instead. Or this:

def randQuickSort2(A): 
    def randQuickSortRec(A,p,r):
        if p<r: 
            q = randPartition(A,p,r)
            randQuickSortRec(A,p,q[0]-1)
            randQuickSortRec(A,q[1]+1,r) 
        return A
    return randQuickSortRec(A,0,len(A)-1)