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

dict_a = {'x' : '1', 'y' : '2'} # 这是赋值
dict_a['z'] = '3' # 这是增加
dict_a['x'] = '4' # 这是改变
dict_a.pop('y')   # 这是删除
'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）

# 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']]
# 这里 states['Michigan'] = MI，而cities['MI'] = detroit
# 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():
    print "%s has the city %s" % (abbrev, city)
# items 是遍历字典内所有元素
# 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', None)
# 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
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

小知识：缩进是4个空格，不是Tab