Binary search implementation

binary_search.py

def binary_search(array, value):
    return _binary_search(array, value, 0, len(array)-1)

def _binary_search(array, value, i, j):
    if i > j:
        return -1

    middle = (i+j)/2

    if array[middle] == value:
        return middle
    elif array[middle] > value:
        return _binary_search(array, value, i, middle)
    return _binary_search(array, value, middle+1, j)

print binary_search(range(19), 100)
print binary_search(range(10), 5)