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18.6: Add, remove, shuffle and sort

  • Page ID
    40841
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    To deal cards, we would like a method that removes a card from the deck and returns it. The list method pop provides a convenient way to do that:

    #inside class Deck:
    
        def pop_card(self):
            return self.cards.pop()
    

    Since pop removes the last card in the list, we are dealing from the bottom of the deck.

    To add a card, we can use the list method append:

    #inside class Deck:
    
        def add_card(self, card):
            self.cards.append(card)
    

    A method like this that uses another method without doing much work is sometimes called a veneer. The metaphor comes from woodworking, where a veneer is a thin layer of good quality wood glued to the surface of a cheaper piece of wood to improve the appearance.

    In this case add_card is a “thin” method that expresses a list operation in terms appropriate for decks. It improves the appearance, or interface, of the implementation.

    As another example, we can write a Deck method named shuffle using the function shuffle from the random module:

    # inside class Deck:
                
        def shuffle(self):
            random.shuffle(self.cards)
    

    Don’t forget to import random.

    As an exercise, write a Deck method named sort that uses the list method sort to sort the cards in a Deck. sort uses the __lt__ method we defined to determine the order.


    18.6: Add, remove, shuffle and sort is shared under a CC BY-NC 3.0 license and was authored, remixed, and/or curated by Allen B. Downey.

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