binary search implementation

binary_search.py

# -*- coding: utf8 -*-


def binary_search(l, value):
    """ (list, object) -> int

    >>> binary_search([1, 2, 3, 4, 5], 3)
    2
    >>> binary_search([1, 2, 3, 4, 5], 5)
    4
    >>> binary_search([1, 2, 3, 4, 5], 8)
    -1

    """
    start_index = 0
    end_index = len(l) - 1

    while(start_index <= end_index):

        m = (start_index + end_index) // 2
        if l[m] < value:
            start_index = m + 1
        else:
            end_index = m - 1

    if start_index == len(l) or l[start_index] != value:
        return -1
    else:
        return start_index


if __name__ == '__main__':
    import doctest
    doctest.testmod()