Binary search returning None at the final execution

Question

I was learning Python for algorithmic purposes. I learned how binary search works and tried to implement it in Python code, without consulting internet. I haven't still looked at how to implement it, I want to make my code work at first. So here is the problem.

The code works fine until the final step where it returns None instead of returning item already in the list. Please instruct me how to correct it. I used pythontutor's online visualizer to visualize the code, and the return value is correct until the final step, where the return value changes to None and I don't understand how. And I also want the "Base case" to return False if item is not in the list and also return the final item (worst case item) at the same time. Please review my code to have these 2 edits.

Here's a link to the code in pythontutor

Below is the code

def binarysearch(array,element):
    mid_index = len(array)//2
    if len(array) == 1 and array[0] == element:
        return element
    elif element == array[mid_index]:
        return element
    elif element > array[mid_index]:
        array = array[mid_index::]
        binarysearch(array,element)
    else:
        array = array[0:mid_index]
        binarysearch(array,element)

print(binarysearch([17,20,26,31,44,54,55,65,77,93],26))

You are discarding the results of the recursive calls, so your outer call just ends and returns the default, `None`. — Martijn Pieters, Nov 05 '16 at 17:51
`binarysearch(array,element)` should be `return binarysearch(array,element)` or you return `None` !! — Jean-François Fabre, Nov 05 '16 at 17:51
Okay that is fixed. But how to also account for the case when element is not in the list in the recursive base case ? — Shrijan Aryal, Nov 05 '16 at 17:56

Binary search returning None at the final execution

0 Answers0