《Python编程快速上手》（五）Python字典和结构化数据

第5章   字典和结构化数据

5.1 字典数据类型

• “字典”的索引可以使用不同数据类型，不止整数
• 字典的索引被称为“键”，键及其关联的值称为“键-值”对
• 字典输入用{} 

【例】

将字典赋给变量myCat，字典的键为'size','color','disposition'。这些键对应的值为'fat','gray','loud'。通过键可访问其值：

字典仍可用整数值作为键（向列表用作下标），但不必从0开始：

5.1.1 字典与列表

• 字典中的表序是不排序的，所以键-值对输入顺序不重要
• 字典中的表序是不排序的，所以不能像列表那样对字典切片
• 不能访问字典中不存在的键
• 字典可用任意值作为键来组织数据

birthdays = {'Alice':'Apr 1','Bob':'Dec 12','Carol':'Mar 4'}

while True:
    print('Enter a name(blank to quit)')
    name = input()
    if name == '':
        break
    if name in birthdays:
        print(birthdays[name] + ' is the birthday of ' + name)
    else:
        print('I do not have birthday information for ' + name)
        print('What is their birthday')
        date = input()
        birthdays[name] = date
        print('Birthday database updated.')

5.1.2 key()、values()、和items()方法

• key()、values()、和items()三个字典方法可返回类似列表的值，分别对应于字典的键、字典的值和字典的键-值，但返回的并不是真正的列表，不能被修改，没有append()等方法。但这些数据类型（dict_keys、dict_values、dict_items）可用于for循环

• list()将keys()返回的dict_keys类型值转化为一个对应列表

5.1.3 检查字典中是否存在键或值

5.1.4 get()方法

• 两个参数：要取得的值的键；若该键不存在时，备用值。

5.1.5 setdefault()方法

• 参数1：要检查的键     参数2：若该键不存在时要设置的值
• 返回键的值

#统计message中各字符出现次数
message = 'It was a bright cold day in April,and the clocks were striking thirteen.'
count = {}
for char in message:
    count.setdefault(char,0)
    count[char] += 1
print(count)

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5.2 漂亮打印

import pprint
message = 'It was a bright cold day in April,and the clocks were striking thirteen.'
count = {}
for char in message:
    count.setdefault(char,0)
    count[char] += 1
pprint.pprint(count)

• 若字典本身包含嵌套的列表或字典，print.print()就很有用
• 希望得到漂亮打印的文本字符串，而不显示。可使用pprint.pformat()

pprint.pprint(count)#等价于print(pprint.pformat(count))

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5.3 使用数据结构对真实世界建模

5.3.1 井字棋盘

theBoard = {'top-L':' ','top-M':' ','top-R':' ',
            'mid-L':' ','mid-M':' ','mid-R':' ',
            'low-L':' ','low-M':' ','low-R':' '}
#╋┏┳┓┫┛┻┗┣┃┃━━
def printBoard(board):
    print(board['top-L']+'|'+board['top-M']+'|'+board['top-R'])
    print('-+-+-')
    print(board['mid-L']+'|'+board['mid-M']+'|'+board['mid-R'])
    print('-+-+-')
    print(board['low-L']+'|'+board['low-M']+'|'+board['low-R'])

turn = 'X'
for i in range(9):
    printBoard(theBoard)
    print('Turn for ' + turn +'. Move on which space?')
    move = input()
    theBoard[move] = turn
    if turn == 'X':
        turn = 'O'
    else:
        turn = 'X'

printBoard(theBoard)

5.3.2 嵌套的字典和列表

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5.4 小结

5.5 习题

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5.6 实践项目

5.6.1 好玩游戏的物品清单

def displayInventory(goods):
    count = 0
    print('Inventory:')
    for i,j in goods.items():             
        print(str(j) + ' ' + i)
        count += j
    print('Total number of items: ' + str(count))

Goods = {'rope':1,'torch':6,'gold coin':42,'dagger':1,'arrow':12}
displayInventory(Goods)

5.6.2 列表到字典的函数，针对好玩游戏物品清单

def addToInventory(inventory,addedItems):
    count = 1
    for i in range(len(addedItems)):
        count = inventory.setdefault(addedItems[i],1)#新物品，值为1，插入
        if count != 1:#原有的物品，更改值 +1
            inventory[addedItems[i]] += 1
    return inventory
        
def displayInventory(goods):
    count = 0
    print('Inventory:')
    for i,j in goods.items():             
        print(str(j) + ' ' + i)
        count += j
    print('Total number of items: ' + str(count))

inv = {'gold coin':42,'rope':1}
dragonLoot = ['gold coin','dagger','gold coin','gold coin','ruby']
inv = addToInventory(inv,dragonLoot)
displayInventory(inv)