10.3 实例研究：乐透数
编写程序决定输入数字是否涵盖了1-99之间的所有整数：
# Create a list of 99 Boolean elements with value False
isCovered = 99 * [False]
endOfInput = False
while not endOfInput:
s = input("Enter a line of numbers separated by spaces: ")
items = s.split()
lst = [eval(x) for x in items]
for number in lst:
if number == 0:
endOfInput = True
else:
isCovered[number - 1] = True
allCovered = True
for i in range(99):
if not isCovered[i]:
allCovered = False
break
if allCovered:
print("The tickets cover all numbers")
else:
print("The tickets don't cover all numbers")
10.4 实例研究：一副扑克牌
在一副扑克牌中随机抽出四张并显示花色与数字:
# Create a deck of cards
deck = [x for x in range(52)]
# Create suits and ranks lists
suits = ["Spades", "Hearts", "Diamonds", "Clubs"]
ranks = ["Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"]
import random
random.shuffle(deck)
for i in range(4):
suit = suits[deck[i] // 13]
rank = ranks[deck[i] % 13]
print("Card number", deck[i], "is the", rank, "of", suit)
10.5 扑克牌图形用户界面
给出一个图形用户界面，单机shuffle按钮，显示四张随机扑克牌的图像：
from tkinter import *
import random
class DeckOfCardsGUI:
def __init__(self):
window = Tk()
window.title("Pick Four Cards Radnomly")
self.imageList = []
for i in range(1, 53):
self.imageList.append(PhotoImage(file = "image/card/" + str(i) + ".gif"))
frame = Frame(window);
frame.pack()
self.labelList = []
for i in range(4):
self.labelList.append(Label(frame, image = self.imageList[i]))
self.labelList[i].pack(side = LEFT)
Button(window, text = "Shuffle", command = self.shuffle).pack()
window.mainloop()
def shuffle(self):
random.shuffle(self.imageList)
for i in range(4):
self.labelList[i]["image"] = self.imageList[i]
DeckOfCardsGUI()
10.6 复制列表
想到复制列表时，你可能会尝试这条语句：
list2 = list1
实际上，这样只是让list2指向list1的一个引用，原list2的内容就成了垃圾，被Python自动收集重新利用。因此此时list2与list1实际上会指向同一块内容。
为了达到真正赋值的效果，可以采用：
list2 = [x for x in list1]
list2 = [] + list1
10.7 将列表传递给函数
）列表传递给函数后值可变
由于列表是一个可变对象，列表的内容可能在函数调用后发生改变：
def main():
x = 1
y = [1, 2, 3]
m(x, y)
print("x is", x)
print("y[0] is", y[0])
def m(number, numbers):
number = 1001
numbers[0] = 5555
main()
该程序运行结果如图所示：
如图，由于函数对简单变量进行传值调用，x的值在函数调用后并不发生改变。而y这个列表的值就发生了改变
）默认参数
Python中的默认参数只会声明一次，亦即生成函数的默认参数后此参数值将一直保留，在后续调用中保留其值：
def add(x, lst = []):
if x not in lst:
lst.append(x)
return lst
def main():
list1 = add(1)
print(list1)
list2 = add(2)
print(list2)
list3 = add(3, [11, 12, 13, 14])
print(list3)
list4 = add(4)
print(list4)
main()
此程序运行结果如下所示：
由此可见，在第二次、第四次调用add()时，原先创建的默认参数lst里的值还存在，故在调用后会累积在列表中。
若想每次调用后默认参数都回到[]，使用如下方法：
def add(x, lst = None):
if lst == None:
lst = []
if x not in lst:
lst.append(x)
return lst
def main():
list1 = add(1)
print(list1)
list2 = add(2)
print(list2)
list3 = add(3, [11, 12, 13, 14])
print(list3)
list4 = add(4)
print(list4)
main()
10.8 从函数返回一个列表
函数返回一个列表时，就会返回这个列表的引用值
10.9 实例研究：统计每个字母的出现次数
随机生成100个小写字母并统计他们出现的频数：
import RandomCharacter
def main():
chars = createList()
print("The lowercase letters are:")
displayList(chars)
counts = countLetters(chars)
print("The occurences of each letter are:")
displayCounts(counts)
def createList():
chars = []
for i in range(100):
chars.append(RandomCharacter.getRandomLowerCaseLetter())
return chars
def displayList(chars):
for i in range(len(chars)):
if (i + 1) % 20 == 0:
print(chars[i])
else:
print(chars[i], end = ' ')
def countLetters(chars):
counts = 26 * [0]
for i in range(len(chars)):
counts[ord(chars[i]) - ord('a')] += 1
return counts
def displayCounts(counts):
for i in range(len(counts)):
if (i + 1) % 10 == 0:
print(counts[i], chr(i + ord('a')))
else:
print(counts[i], chr(i + ord('a')), end = ' ')
main()