Design of Computer Programs L1

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第一讲主要是做一个扑克牌游戏，主要是扑克牌规则的设计。复用了max函数。涉及到了重构和测试的概念，以及在程序编写过程中需要注意Correctness，effeciency, feature和elegance四方面。以下是较完整代码：

import random


def poker(hands):
    """Return a list of winning hands: poker([hand,...]) => [hand,...]"""
    return allmax(hands, key=hand_rank)


def allmax(iterable, key=None):
    """Return a list of all items equal to the max of the iterable."""

    # maxv = hand_rank(max(iterable, key=key))
    # maxl = []
    # for item in iterable:
    #     if hand_rank(item) == maxv:
    #         maxl.append(item)
    # return maxl if len(maxl) > 0 else None

    result, maxval = [], None
    key = key or (lambda x: x)
    for x in iterable:
        xval = key(x)
        if not result or xval>maxval:
            result, maxval = [x], xval
        elif xval == maxval:
            result.append(x)
    return result

def hand_rank(hand):
    "Return a value indicating the ranking of a hand."
    ranks = card_ranks(hand)
    if straight(ranks) and flush(hand):
        return (8, max(ranks))
    elif kind(4, ranks):
        return (7, kind(4, ranks), kind(1, ranks))
    elif kind(3, ranks) and kind(2, ranks):
        return (6, kind(3, ranks), kind(2, ranks))
    elif flush(hand):
        return (5, ranks)
    elif straight(ranks):
        return (4, max(ranks))
    elif kind(3, ranks):
        return (3, kind(3, ranks), ranks)
    elif two_pair(ranks):
        return (2, two_pair(ranks), ranks)
    elif kind(2, ranks):
        return (1, kind(2, ranks), ranks)
    else:
        return (0, ranks)

def card_ranks(hand):
    "Return a list of the ranks, sorted with higher first."
    ranks = ['--23456789TJQKA'.index(r) for r, s in hand]
    ranks.sort(reverse = True)
    return [5, 4, 3, 2, 1] if (ranks == [14, 5, 4, 3, 2]) else ranks

def flush(hand):
    "Return True if all the cards have the same suit."
    suits = [s for r,s in hand]
    return len(set(suits)) == 1

def straight(ranks):
    "Return True if the ordered ranks form a 5-card straight."
    return (max(ranks)-min(ranks) == 4) and len(set(ranks)) == 5

def kind(n, ranks):
    """Return the first rank that this hand has exactly n-of-a-kind of.
    Return None if there is no n-of-a-kind in the hand."""
    for r in ranks:
        if ranks.count(r) == n: return r
    return None

def two_pair(ranks):
    "If there are two pair here, return the two ranks of the two pairs, else None."
    pair = kind(2, ranks)
    lowpair = kind(2, list(reversed(ranks)))
    if pair and lowpair != pair:
        return (pair, lowpair)
    else:
        return None

def test():
    "Test cases for the functions in poker program."
    sf1 = "6C 7C 8C 9C TC".split() # Straight Flush
    sf2 = "6D 7D 8D 9D TD".split() # Straight Flush
    fk = "9D 9H 9S 9C 7D".split() # Four of a Kind
    fh = "TD TC TH 7C 7D".split() # Full House
    assert poker([sf1, sf2, fk, fh]) == [sf1, sf2]
    # print(hand_rank(max([sf1, sf2], key=hand_rank)))
    print('tests pass')


mydeck = [r+s for r in '23456789TJQKA' for s in 'SHDC']

def deal(numhands, n=5, deck=mydeck):
    """发牌"""
    # hands = []
    # for handindex in range(numhands):
    #     hand = []
    #     for i in range(n):
    #         temp = random.choice(deck)
    #         hand.append(temp)
    #         deck.remove(temp)
    #     hands.append(hand)
    # return hands
    random.shuffle(deck)
    return [deck[n*i:n*(i+1)] for i in range(numhands)]

Knuth's Algorithm P.

import random


def shuffle(deck):
    """Knuth's Algorithm P."""
    n = len(deck)
    for i in range(n-1):
        swap(deck, i, random.randrange(i, n))


def swap(deck, i, j):
    """Swap elements i and j of a collection"""
    deck[i], deck[j] = deck[j], deck[i]

此部分在最后讲了纯函数的概念，纯函数是做计算（computing)的函数，返回计算结果，便于测试。而另一类函数是Doing类，表示一些过程指令，无返回值，所以难于测试。（是不是类似函数式编程中的纯函数？）

HW1

HW1

HW2

HW2