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Learn Python The Hard Way学习(39) - 可爱的字典

2012-07-03

下面我们学习另外一种常用的容器:字典。python叫dict,有的语言叫hash,我都会使用到,这些都不是重点,重点是它和list的区别。我们这样使用list:>>> things = ['a', 'b', 'c', ...

下面我们学习另外一种常用的容器:字典。

python叫dict,有的语言叫hash,我都会使用到,这些都不是重点,重点是它和list的区别。我们这样使用list:
>>> things = ['a', 'b', 'c', 'd']
>>> print things[1]
b
>>> things[1] = 'z'
>>> print things[1]
z
>>> print things
['a', 'z', 'c', 'd']

我们可以在list中使用索引,就是说我们可以通过数字找到list中的元素。

而dict不仅仅可以使用数字,还可以使用任何东西找到元素,看下面的例子:
>>> stuff = {'name': 'Zed', 'age': 36, 'height': 6*12+2}
>>> print stuff['name']
Zed
>>> print stuff['age']
36
>>> print stuff['height']
74
>>> stuff['city'] = "san Francisco"
>>> print stuff['city']
san Francisco
>>>

我们可以用一个字符串为字典插入数据,也能使用数字,比如:
>>> 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}
>>>

当然,字典不可能只可以插入数据,可以删除数据:
>>> del stuff['city']
>>> del stuff[1]
>>> del stuff[2]
>>> stuff
{'name': 'Zed', 'age': 36, 'height': 74}
>>>

下面做一个练习:
[python]
# 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 same 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():
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', None)


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


运行结果
root@he-desktop:~/mystuff# python ex39.py
----------
NY State has: New York
OR State has: Portland
----------
Michigan's abbreviation is: MI
Florida's abbreviation is: FL
----------
Michigan has: Detroit
Florida has: Jacksonville
----------
California is abbreviated CA
Michigan is abbreviated MI
New York is abbreviated NY
Florida is abbreviated FL
Oregon is abbreviated OR
----------
FL has the city Jacksonville
CA has the city San Francisco
MI has the city Detroit
OR has the city Portland
NY has the city New York
----------
California state is abbreviated CA and has city San Francisco
Michigan state is abbreviated MI and has city Detroit
New York state is abbreviated NY and has city New York
Florida state is abbreviated FL and has city Jacksonville
Oregon state is abbreviated OR and has city Portland
----------
Sorry, no Texas.
The city for the state 'TX' is: Does Not Exist

加分练习
1. 用你当地的城市做这个练习。

2. 在python文档中找到字典的介绍,看看还能做些什么

3. 看看有什么是字典不能做的,主要是字典是无序的。
作者:lixiang0522


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