def string_to_list(time):
    """Takes a time given in hh:mm:ss format and returns a list
    ['h','h','m','m','s','s'].
    Parameters:
    time: string format 'hh:mm:ss' 
    """
    new_time = ''
    for letter in time:
        if letter != ':':
            new_time += letter
    new_time = list(new_time)
    if len(new_time) != 6:
        raise RuntimeError('Time list is not of length 6')
    return new_time
