def duration_string_to_seconds(string):
    """ Converts a string representation of duration
        into total seconds in float.

        >>>  duration_string_to_seconds('00:03:16')
        196
    """
    duration = string.split(':')
    return int(duration[0]) * 60 * 60 + int(duration[1]) * 60 + int(duration[2]
        )
