binary_search.py

def binary_search(target_array, target, first, last):

    #If the array is empty return -1
    if not len(target_array):
        return -1
    #if the array has only one element in it, check that element. 
    elif len(target_array) == 1:
        if target_array[0] == target:
            return 0
        else:
            return -1

    #If last is less than first you probably don't have a hit. 
    if last >= first:

        mid = first + (last - first) / 2

        if target_array[mid] == target:
            return mid
        elif target_array[mid] > target:
            return binary_search(target_array, target, first, mid - 1)
        else:
            return binary_search(target_array, target, mid + 1, last)
    else:
        return -1