字典和结构化数据

• keys()、values()、items()返回字典的键、值、键值对

>>> spam = {'color':'red','age':42 }
>>> for k in spam.keys():
            print(k)
color
age
>>> for v in spam.values():
            print(v)
red
42
>>> for k, v in spam.items():
          print('key: ' + k +' values: ' + str(v))
key: color values: red
key: age values: 42

• 检查字典中是否存在键或值

>>> spam = {'name':'zophie','age':7}
>>> 'name' in spam.keys()
True
>>> 'zophie' in spam.values()
True
>>> 'color' in spam.keys()
False
>>> 'color' not in spam.keys()
True
>>> 'color' in spam
False

'color' in spam 是一个简写版本，相当于'color' in spam.keys()

• get()方法
  有两个参数：要取得其值的键，以及如果该键不存在时，返回的备用值。避免键不存在时产生KeyError报错。

>>> picnic_items = {'apples':5,'cups':2}
>>> 'I am bringing ' + str(picnic_items.get('cups',0) + ' cups'.)
'I am bringing 2 cups.
>>>  'I am bringing ' + str(picnic_items.get('eggs',0) + ' eggs'.)
'I am bringing 0 eggs.

• setdefault()方法
  有两个参数，第一个是要检查的键，第二个是如果键不存在时要设置的值。如果该键确实存在，方法就返回键的值。

>>> spam = {'name':'pooka','age':5}
>>> spam.setdefault('color','black')
black
>>> spam
{'name':'pooka','age':5','color':'black'}
>>> spam.setdefault('color','white')
black

• 计算一个字符串中每个字符出现的次数

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

print(count)

import pprint
pprint.pprint(count)

print(pprint.pformat(count))

漂亮打印，导入pprint模块，pprint()和pformat()函数

• 一个小程序，按格式显示一个变化的游戏物品清单。

import pprint
#导入漂亮打印pprint模块
inv = {'gold coin':42,'rope':1} # 原有物品清单
dragonLoot = ['gold coin','dagger','gold coin','gold coin','ruby'] # 刷一个副本获取的战利品

def addToInventory(inventory,addedItems): # 包含两个参数，原有清单（字典）和新增物品（列表）
    """将新获取的战利品增加到原物品清单中"""
    for i in addedItems:
        inventory.setdefault(i,0)
        inventory[i] += 1
    pprint.pprint(inventory) #漂亮打印
    return inventory #返回最终清单

spam = addToInventory(inv,dragonLoot)
print(spam)

def displayInventory(inventory):
    """按照格式显示物品清单和物品总数"""
    print('Inventory:')
    item_total = 0
    for k,v in inventory.items():
        print(str(v) + ' ' + k)
        item_total += v
    
    print('Total number of items:' + str(item_total))

displayInventory(spam)

输出
{'dagger': 1, 'gold coin': 45, 'rope': 1, 'ruby': 1}
{'gold coin': 45, 'rope': 1, 'dagger': 1, 'ruby': 1}
Inventory:
45 gold coin
1 rope
1 dagger
1 ruby
Total number of items:48