Recursive binary search in Python

recursive_binary_search.py

def get_index_recursive(vector, number, index = -1, prior_index = 0):

    index_helper = index if index > -1 else int(len(vector)/2)

    if vector[index_helper] < number:
        prior_index_helper = prior_index if prior_index > 0 else len(vector)
        index_helper = int((prior_index_helper - index_helper)/2) + index_helper
    elif vector[index_helper] >  number:
        prior_index_helper = index_helper +1
        index_helper = int(index_helper/2)
    else:
        return index_helper

    return get_index_recursive(vector, number, index_helper, prior_index_helper)