TypeError: unsupported operand type(s) for -: 'str' and 'int' (Python)

Question

I have written the code for quick sort in python, but this code is throwing an error.

----------


    k=0
    def partition(arr,low_index,high_index):
        key = arr[low_index]
        i = low_index + 1;
        j = high_index

        while True:
            while (i<high_index and key>=arr[i]):
                i+=1
            while (key<arr[j]):
                j-=1
            if i<j:
                arr[i,j] = arr[j,i]
            else:
                arr[low_index,j]=arr[j,low_index]
                return j

    def quicksort(arr,low_index,high_index):
         if low_index < high_index:
            j = partition(low_index,high_index,arr)
            print("Pivot element with index "+str(j)+" has thread "+str(k))
            if left<j:
                k=k+1
                quicksort(arr,low_index, j - 1)
            if i<right:
                k=k+1
                quicksort(arr,j+1,high_index)
         return arr

    n = input("Enter the value n ")
    arr=input("Enter the "+str(n)+" no. of elements ")
    brr=quicksort(arr,0,n-1)
    print("Elements after sorting are "+str(brr))

----------

The error it is throwing is

Enter the value n 4

Enter the 4 no. of elements [5,6,2,7] Traceback (most recent call last): File "C:\\Users\\devendrabhat\\Documents\\dev\\dev\\quick.py", line 38, in brr=quicksort(arr,0,n-1) TypeError: unsupported operand type(s) for -: 'str' and 'int'

Answer 1

You need to change n to an integer, not a string. Your error is telling you, that you are trying to perform an operation (- in this case) on a string and an integer. Change str(n) to int(n) so you have the same type throughout.

Answer 2

you are declaring 'n' as string there in your code. And trying to perform arithmetic operation with string.

So it is giving that error. Change this str(n) to int(n) .

It will work !!!

Answer 3

n is string. So you need to change it to int:

n = int(n)

If you input [5,6,2,7] on line 37, python interpret it as string like "[5,6,2,7]". So, you need to convert string to list.

arr = eval(arr)