def find_different_char_index(start_string, edit_string):
    """Compares standard and modified string and identifies the index of the modified character
        ex: find_char_difference_index("CCAGG","CFAGG") = 1

    :param start_string: starting string
    :param edit_string: string with a single character edit from start_string
    :return: index of string difference
    """
    assert len(start_string) == len(edit_string), ""
    pos = [i for i in range(len(start_string)) if start_string[i] != edit_string[i]]
    assert len(pos) == 1, "Only one character difference allowed. " \
                          "start_string={}, edit_string={}".format(start_string, edit_string)
    return pos[0]