exercise 39 字典

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本文介绍了Python中list和dictionary的基本操作，包括元素的增删改查，并通过实例展示了如何使用这两种数据结构来解决实际问题。

简单介绍：

list的使用：

>>> things = ['a', 'b', 'c', 'd']
>>> print things[1]
b
>>> things[1] = 'z'
>>> print things[1]
z
>>> things
['a', 'z', 'c', 'd']

dictionary的使用：

>>> stuff = {'name': 'Zed', 'age': 39, 'height': 6 * 12 + 2} #列表使用方括号[ ] 字典使用大括号{ }
>>> print stuff['name']
Zed
>>> print stuff['age']
39
>>> print stuff['height']
74
>>> stuff['city'] = "San Francisco"
>>> print stuff['city']
San Francisco

使用一个字符串为字典插入数据：

>>> stuff[1] = "Wow"

>>> stuff[2] = "Neato"

>>> print stuff[1]

Wow

>>> print stuff[2]

Neato

>>> print stuff

{'city': 'san Francisco', 2: 'Neato', 'name': 'Zed', 1: 'Wow', 'age': 36, 'height': 74} #为什么插入位置是这个鬼样子呢？？

删除数据：

>>> del stuff['city']

>>> del stuff[1]

>>> del stuff[2]

>>> stuff

{'name': 'Zed', 'age': 36, 'height': 74}

>>>

练习：

# create a mapping of state to abbreviation
states= {
    "Oregon": "OR",
    "Florida": "FL",
    "California": "CA",
    "New York": "NY",
    "Michigan": "MI"
}

# create a basic set of states and some cities in them
cities = {
    'CA': 'San Francisco',
    'MI': 'Detroit',
    'FL': 'Jacksonville'
}

# add some more cities
cities['NY'] = 'New York'
cities['OR'] = 'Portland'

# print out some cities
print '-' * 10
print "NY State has: ", cities['NY']
print "OR State has: ", cities['OR']

# print some states
print '-' * 10
print "Michigan's abbreviation is: ", states['Michigan']
print "Florida's abbreviation is: ", states['Florida']

# do it by using the state then cities dict
print '-' * 10
print "Michigan has: ", cities[states['Michigan']]
print "Florida has: ", cities[states['Florida']]

# print every state abbreviation
print '-' * 10
for state, abbrev in states.items():   
    print "%s is abbreviated %s" % (state, abbrev)

# print every city in state
print '-' * 10
for abbrev, city in cities.items():    #Python 字典(Dictionary) items() 函数以列表返回可遍历的(键, 值) 元组数组。
    print "%s has the city %s" % (abbrev, city)

# now do both at the same time
print '-' * 10
for state, abbrev in states.items()

    print "%s state is abbreviated %s and has city %s" % (
        state, abbrev, cities[abbrev])

print '-' * 10
# safely get a abbreviation by state that might not be there
state = states.get('Texas')            # dict.get(key, default=None)  总结中有例子

if not state:
    print "Sorry, no Texas."

# get a city with a default value
city = cities.get('TX', 'Does Not Exist')
print "The city for the state 'TX' is: %s" % city

编程细节：

1、字典用大括号，每个数据之间用逗号隔开，最后一个不用逗号

2、加入新数据的时候如下格式；用方括号里面的内容作为索引。

cities['NY'] = 'New York'

3、

print 'NY state has: ' , cities['NY']  ##中间有逗号！！！ 前面没有%x的符号，后面不需要加%

4、

5、

总结：

1.获取字典值有两种方法，一个是通过dict['key'], 另一个是dict.get()方法。

dict.get(key,default=None)

eg:

>>> info ={'1':'first','2':'second','3':'third'}
>>> number =raw_input('input type you number:')
input 
type you number:3
>>> printinfo.get(number,'error')
third
>>> number =raw_input('input type you number:')
input 
type you number:4
>>> printinfo.get(number,'error')
error

2. dict.items()用法：

Python 字典(Dictionary) items() 函数以列表返回可遍历的(键, 值) 元组数组。

eg：

dict = {'Name': 'Zara', 'Age': 7}

print "Value : %s" %  dict.items()

输出：

Value : [('Age', 7), ('Name', 'Zara')]   # reverse order when output

Study Drill:

列表和字典的区别:

列表长用于已经排好顺序的元素中，字典是为了匹配关键字和数值

A list is for an ordered list of items. A dictionary (or dict) is for matching some items (called "keys") to other items (called "values").

3.collections.OrderedDict

OrderedDict 有序字典

OrderedDict是dict的子类，它记住了内容添加的顺序。
比较时，OrderedDict要内容和顺序完全相同才会视为相等