Here's how you can track the index of your recursive function in Python!

"""This example is made to track the index of the value that we
are returning. To return, track, or modify any value in a
recursive manner, the value must be passed into the
function as an argument each time the function is
recursively called."""


def recursive_binary_search(values, target, index=None, count=1):

    if len(values) == 0:
        return False

    midpoint = len(values)//2
    # Showing the path traveled by the algorithm.
    print("This is our midpoint during run {}: {}"
          .format(count, values[midpoint]))

    if index is None:
        index = (len(values)//2)
    print("-- This is our index during run {}: {}\n"
          .format(count, index))

    if values[midpoint] == target:
        print("The value was {} and it took {} tries to find."
              .format(values[midpoint], count))
        print("The index was {}.".format(index))
        return True

    if values[midpoint] < target:
        new_list = values[midpoint+1:]
        index += (len(new_list)//2 + 1)
        return recursive_binary_search(new_list, target, index, count+1)

    else:
        new_list = values[:midpoint]
        # This is to ensure that the index is calculated correctly,
        #  regardless of whether the len//2 is odd or even.
        index -= (len(new_list)//2) if (len(new_list) % 2 == 0) else (len(new_list)//2 + 1)
        return recursive_binary_search(new_list, target, index, count+1)


# This calls the function on a range of numbers from 1 to 100.
# Change the second number to change the value searched for.
recursive_binary_search(range(1, 101), 99)