then what must be used ?

Not a kata issue, your function is returning None or not returning and that's the default return value for Python. You can see in the kata description that False is the expected value for those input values.

Also take note of the edge case - if both strings are empty then you should return false/False.

I got everything right except for the last sample test is_opposite("" , "") keeps giving a NONE SHOULD BE FALSE.

I faced the same issue why is there a not.

Do you see the single quotes there? You're returning strings instead of numbers.

I changed what you suggested and I still cant get the tests to go through, look at the test results:

Test Results:
Fixed tests
Tests
should return 1 litre: '1' should equal 1
Test Passed
should return 6 litres: '6' should equal 6
Test Passed
should return 5 litres: '5' should equal 5
should return 893 litres: '893' should equal 893
Test Passed

inexplicable lol.

Your function is printing the result instead of returning it, and also, you don't need to add that string to it, only return the number.

using round() function in python doesnt help

Read the error message:

ValueError: invalid literal for int() with base 10: 'n'

You can't convert a letter to an int, that's what it is about.

n is an integer I did convert it into an integer. I cant seem to find my problem.
Here is my code:
def f(n):
return sum(range(0,int(n)+1))

It's your duty to verify that n is a valid positive integer number.

You code only passes 4 tests (there are more), not a kata issue.

Try this one in sample tests:

test.assert_equals(f('n'), None)

6 maybe in the string format