笨方法学Python——习题39

dict 字典{ }：用单引号把Key与Value标记，用 : 连接，‘Key’ ：‘Value’ 是一个字典元素，调用x['Key']可获取Value值

1 dict_a = {'x' : '1', 'y' : '2'} # 这是赋值
2 dict_a['z'] = '3' # 这是增加
3 dict_a['x'] = '4' # 这是改变
4 dict_a.pop('y')   # 这是删除
5 'z' in dict_a     # 判断是否存在 True  False

list 列表[ ]：append( )增加、list_a.insert(1,'x')：在指定位置增加、list_a.pop()默认删除最后一位，可指定

tuple元组( )：不可更改，但可以把列表插入元组，通过改变元组中列表元素，进行变更

set ：类似于dict，也是一组Key的集合，但不存储Value，由于Key不能重复，故无重复（自动过滤）

 1 # create a mapping of state to abbreviation
 2 states = {
 3     'Oregon': 'OR',
 4     'Florida': 'FL',
 5     'California': 'CA',
 6     'New York': "NY",
 7     'Michigan': 'MI'
 8 }
 9 
10 # create a basic set of states and some cities in them
11 cities = {
12     'CA': 'San Francisco',
13     'MI': 'Detroit',
14     'FL': 'Jacksonville'
15 }
16 
17 # add some more cities
18 cities['NY'] = 'New York'
19 cities['OR'] = 'Portland'
20 
21 # print out some cities
22 print '-' * 10
23 print "NY State has: ", cities['NY']
24 print "OR State has: ", cities['OR']
25 
26 # print some states
27 print '-' * 10
28 print "Michigan's abbreviation is: ",states['Michigan']
29 print "Florida's abbreviation is: ", states['Florida']
30 
31 # do it by using the state then cities dict
32 print '-'* 10
33 print "Michigan has: ", cities[states['Michigan']]
34 print "Florida has: ", cities[states['Florida']]
35 # 这里 states['Michigan'] = MI，而cities['MI'] = detroit
36 # print every state abbreviation
37 print '-' * 10
38 for state, abbrev in states.items():
39     print "%s is abbreviated %s" % (state, abbrev)
40 
41 # print every city in state
42 print '-' * 10
43 for abbrev, city in cities. items():
44     print "%s has the city %s" % (abbrev, city)
45 # items 是遍历字典内所有元素
46 # now do both at the same time
47 print '-' * 10
48 for state, abbrev in states.items():
49     print "%s state is abbreviated %s and has city %s" % (state, abbrev, cities[abbrev])
50 
51 
52 print '-' * 10
53 # safely get a abbreviation by state that might not be there
54 state = states.get('Texas', None)
55 # get 作用与 in 类似，都是判断是否存在，如果存在，则正常打印，如果不存在，返回指定值
56 if not state:
57     print "Sorry, no Texas."
58 
59 # get a city with a default value
60 city = cities.get('TX', 'Does Not Exist')
61 print "The city for the state 'TX' is: %s" % city

小知识：缩进是4个空格，不是Tab