字典（dict）

1.定义

eng2sp = {}   # 定义空字典
eng2sp['one'] = 'uno'
eng2sp['two'] = 'dos'
print eng2sp
print eng2sp['two']        # 字典查询：通过key查询value
eng2sp[2] = 'hdi'          # 字典没有顺序
print eng2sp

2.常见操作

inventory = {'apples': 430, 'bananas': 312,'oranges': 525, 'pears': 217}
# 修改
inventory['bananas'] = 0
print inventory
# 删除
del inventory['bananas']
print inventory
# 计数
print len(inventory)
# 清空
inventory.clear()
print inventory

3.别名和拷贝

inventory = {'apples': 430, 'bananas': 312,'oranges': 525, 'pears': 217}
alias = inventory
copy1 = inventory.copy()                #alias和inventory指向同一个值。而copy1则指向全新的拷贝
alias['bananas'] = 33
print inventory['bananas']              #如果修改alias，inventory也发生变化。
copy1['bananas'] = 56
print inventory['bananas']              #如果修改copy1，inventory则不会发生变化。

4.get用法

letterCounts = {}
for letter in "Mississippi":
    letterCounts[letter] = letterCounts.get (letter, 0) + 1
print letterCounts          #打印出每个字母出现的次数