TypeError: can only concatenate str (not "int") to str SUM

Question

I am trying to make a program that will sum the cube of a number up to an upper boundary.

The mathematical formula is (n*(n+1)/2)^2

My code in Python:

def cube_numbers():
   upper_boundary = 0
   cube_sum = 0
   upper_boundary = input("Please enter the upper boundary:")
   cube_sum = ((upper_boundary * (upper_boundary + 1) / 2)**2)
   print("The sum of the cube of numbers up to" & upper_boundary & "is" & cube_sum)
#main
cube_numbers()

But I get the following error:

  Traceback (most recent call last):

  File "C:/Users/barki/Desktop/sum of cubes.py", line 10, in <module>
    cube_numbers()

  File "C:/Users/barki/Desktop/sum of cubes.py", line 5, in cube_numbers
    cube_sum = ((upper_boundary * (upper_boundary + 1) / 2)**2)
TypeError: can only concatenate str (not "int") to str

Once again: `input(..)` returns a `str`ing, not an `int`, use `upper_boundary = int(upper_boundary)` to convert it to an `int`. — Willem Van Onsem, Oct 06 '18 at 19:32
local variable 'upper_boundary' referenced before assignment — , Oct 06 '18 at 19:33
**after** you assigned it with `input(..)` of course... I'm quite cursious why you tink you can call a function on a not yet assigned variable? — Willem Van Onsem, Oct 06 '18 at 19:34
well some languages allow to call a function with variables that are defined later, so I'm not saying you're an idiot :) — Willem Van Onsem, Oct 06 '18 at 19:51
Possible duplicate of [TypeError: Can only concatenate str (not "int") to str (simple Python programme)](https://stackoverflow.com/questions/52225721/typeerror-can-only-concatenate-str-not-int-to-str-simple-python-programme) — greybeard, Oct 06 '18 at 21:19

score 3 · Accepted Answer · answered Oct 06 '18 at 19:40

The purpose of your function should not be to print. Also it would be better to move your input prompt out of your function and then pass that value into your function. What we can do then is get the input for upper_boundary as an int and then pass that to cube_numbers. That return value will now be cube_sum and we can use formatted printing to print out the statment.

def cube_numbers(x):
    y = int(((x * (x + 1) / 2)**2))
    return y

upper_boundary = int(input("Please enter the upper boundary: "))
cube_sum = cube_numbers(upper_boundary)

print('The sum of the cube of numbers up to {} is {}.'.format(upper_boundary, cube_sum))
# The sum of the cube of numbers up to 10 is 3025.

score 0 · Answer 2 · answered Oct 06 '18 at 20:38

print("The sum of the cube of numbers up to" & upper_boundary & "is" & cube_sum)

You should format your code properly, either by using .format notation or separating different values by , or conacatinating them by converting integer type values to string using str (not recommended)

Always use the .format notation for formatting.

example,

print("The sum of the cube of numbers up to {} is {}".format(upper_boundary, cube_sum))

You can also use indexing for formatting:

example,

print("The sum of the cube of numbers up to {0} is {1}".format(upper_boundary, cube_sum))

In this case whatever is at the first place inside the format method will take the "0th" place in the string.

Another way to do this is by actually supplying some names as the placeholder:

example,

print("The sum of the cube of numbers up to {upper_bnd} is {cube_sm}".format(upper_bnd = upper_boundary, cube_sm = cube_sum))

Hope this helps.

TypeError: can only concatenate str (not "int") to str SUM

2 Answers2