Python中字典有什么用

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1、字典的概念

在Python 中，字典這種數(shù)據(jù)類型的英文叫做 “dict”，有的語言里它的名稱是 “hash”。字典是編程中最常用的數(shù)據(jù)結構之一。它是用來做映射或者存儲你需要的鍵值對，這樣當你需要的時候，你可以通過key來獲取它的值。同樣，程序員不會使用一個像“字典”這樣的術語，來稱呼那些不能像一個寫滿詞匯的真實字典正常使用的事物，所以我們只要把它當做真實世界中的字典來用就好。

2、字典與列表的區(qū)別

針對列表你可以做這樣的事情：

>>> things = ['a', 'b', 'c', 'd']

>>> print things[1]

b >>> things[1] =

'

z'

>>> print things[1]

z >>> things

['a', 'z', 'c', 'd']

你可以使用數(shù)字作為列表的索引，也就是你可以通過數(shù)字找到列表中的元素。你現(xiàn)在應該了解列表的這些特性，而你也應了解，你也只能通過數(shù)字來獲取列表中的元素。而 dict是讓你可以通過任何東西找到元素，不只是數(shù)字。是的，字典可以將一個物件和另外一個東西關聯(lián)，不管它們的類型是什么，我們來看看：

>>> stuff = {'name': 'Zed', 'age': 39, 'height': 6 * 12 + 2}

>>> print stuff['name']

Zed

>>> print stuff['age']

39

>>> print stuff['height']

74

>>> stuff['city'] = "San Francisco"

>>> print stuff['city']

San Francisco

3、字典的使用

除了通過數(shù)字以外，我們還可以用字符串來從字典中獲取 stuff ，我們還可以用字符串來往字典中添加元素。當然它支持的不只有字符串，我們還可以做這樣的事情：

>>> stuff[1] = "Wow"

>>> stuff[2] = "Neato"

>>> print stuff[1]

Wow

>>> print stuff[2]

Neato

>>> stuff

{'city': 'San Francisco', 2: 'Neato', 'name': 'Zed', 1: 'Wow', 'age': 39, 'height': 74

}

這段代碼中，使用了數(shù)字，當打印stuff的時候，不止有數(shù)字還有字符串作為字典的key。當然了，一個只能放東西進去的字典是沒啥意思的，所以我們還要有刪除的方法，也就是使用del這個關鍵字：

>>> del stuff['city']

>>> del stuff[1]

>>> del stuff[2]

>>> stuff

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

4、實例練習

# 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():

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')

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

你看到的結果：

$ 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

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