python – array length variable keeps changing into a 'none type'

January 12, 2022

So I’ve been trying to make a program that uses binary search for school, however whenever I try to run it, it comes back with an error of ‘TypeError: list indices must be integers or slices, not NoneType’

This is the code:

arr = [1,2,3,4,5,6,7]
find = 3
if len(arr)%2 != 0:
    half = int(len(arr)+1)
else:
    half = int(len(arr))
half = half/2
half = int(half)

while True:
    half = int(half)
    sort = arr[half]
    print(sort)
    if find < sort:
        half = print(half/2)
    elif find > sort:
        half = half+(half/2)
    elif find == sort:
        print(f"found at position {half}")

I clearly state that it is an integer, but it just doesn’t work and I don’t know why

>Solution :

Your problem is the line half = print(half/2). print is a function that doesn’t return anything (therefore it returns None), and you are assigning None to half then. You probably mean half = half/2, and if you want to print it, do so on the next line.

Also, take a look at the difference between / and // in python. If you use // to divide by two, it will always return an integer and you won’t need to manually convert it to an int using half = int(half).