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'

Possible duplicate of TypeError: unsupported operand type(s) for /: 'str' and 'int' — Shubham Verma
– Shubham Verma, Commented Feb 14, 2017 at 7:08
Python receives input as a string. You need to use the function int() on that input to turn it into an integer and catch possible exceptions. — MKesper
– MKesper, Commented Feb 14, 2017 at 7:17

Hironsan · Accepted Answer · 2017-02-14 07:16:47Z

2

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)

answered Feb 14, 2017 at 7:16

Hironsan

6851 gold badge5 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

MKesper Over a year ago

Use try and except ValueError, without it's not a complete solution.

Hironsan Over a year ago

If you give a string to eval function, the string is parsed and evaluated as a Python expression. So, if you give a list as string like “[5,6,2,7]”, it is parsed and evaluated. As a result, you can get list object like [5,6,2,7]. If you want to know eval in detail, please look at following site. docs.python.org/3/library/functions.html#eval

Wombatz Over a year ago

Calling eval() directly on the unfiltered value from input() is one of the worst ideas ever. At least use literal_eval from the ast module.

Nick H · Accepted Answer · 2017-02-14 07:12:44Z

2

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.

answered Feb 14, 2017 at 7:12

Nick H

1,0799 silver badges13 bronze badges

Comments

Venkatesh_CTA · Accepted Answer · 2017-02-14 07:38:28Z

1

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 !!!

answered Feb 14, 2017 at 7:38

Venkatesh_CTA

12010 bronze badges

Collectives™ on Stack Overflow

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

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related