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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def open_cards(filename=None):
 """ Open cards from a txt file. :arg str filename: The filename of the deck file to open. If no filename given, defaults to "cards-YYYYMMDD.txt", where "YYYYMMDD" is the year, month, and day. For example, "cards-20140711.txt". :returns: The opened cards, as a list. """

    filename = filename or "cards-%s.txt" % (time.strftime("%Y%m%d"))

    with open(filename, "r") as deck_file:
        card_data = [line.rstrip("\n") for line in deck_file.readlines()]

    cards = [None] * len(card_data)

    for i, card in enumerate(card_data):
        card = card.split()
        cards[i] = Card(card[0], card[1])

    return cards