def show_hidden_word(secret_word, old_letters_guessed):
    """
     this function shows the player his progress in the game
    :param secret_word: the word the player has to guess
    :param old_letters_guessed: all the characters the player has already guessed
    :type secret_word: str
    :type old_letters_guessed: list
    :return: a string which consists of letters and underlines
            the string displays the letters from the old_letters_guessed list that
            are in the secret_word string in their appropriate position,
            and the rest of the letters in the string (which the player has not yet guessed) as underlines
    :rtype: str
    """
    returned_string = ""
    for char in secret_word:
        if char in old_letters_guessed:
            returned_string += char
        else:
            returned_string += "_"
    return " ".join(returned_string)