《python 从入门到精通》§4 字典

§4 字典

2009-8-16

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phonebook = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}

key具有唯一性

 

函数：

>>> items = [('name', 'Gumby'), ('age', 42)]

>>> d = dict(items)

>>> d

{'age': 42, 'name': 'Gumby'}

>>> d['name']

'Gumby'

 

>>> d = dict(name='Gumby', age=42)

>>> d

{'age': 42, 'name': 'Gumby'}

 

基本操作：

       ? len(d) returns the number of items (key-value pairs) in d.

? d[k] returns the value associated with the key k.

? d[k] = v associates the value v with the key k.

? del d[k] deletes the item with key k.

? k in d checks whether there is an item in d that has the key k.

 

       key可以为不变的类型。

       自动添加

      

       >>> x = {}

>>> x[42] = 'Foobar'

>>> x

{42: 'Foobar'}

 

实例：

 

# A simple database

 

# A dictionary with person names as keys. Each person is represented as

# another dictionary with the keys 'phone' and 'addr' referring to their phone

# number and address, respectively.

 

people = {

 

    'Alice': {

        'phone': '2341',

        'addr': 'Foo drive 23'

    },

 

    'Beth': {

        'phone': '9102',

        'addr': 'Bar street 42'

    },

 

    'Cecil': {

        'phone': '3158',

        'addr': 'Baz avenue 90'

    }

 

}

 

# Descriptive labels for the phone number and address. These will be used

# when printing the output.

labels = {

    'phone': 'phone number',

    'addr': 'address'

}

 

name = raw_input('Name: ')

 

# Are we looking for a phone number or an address?

request = raw_input('Phone number (p) or address (a)? ')

 

# Use the correct key:

if request == 'p': key = 'phone'

if request == 'a': key = 'addr'

 

# Only try to print information if the name is a valid key in

# our dictionary:

if name in people: print "%s's %s is %s." % \

    (name, labels[key], people[name][key])

   

    运行结果：

    Name: Beth

Phone number (p) or address (a)? p

Beth's phone number is 9102.

 

格式化输出：

>>> phonebook

{'Beth': '9102', 'Alice': '2341', 'Cecil': '3258'}

>>> "Cecil's phone number is %(Cecil)s." % phonebook

"Cecil's phone number is 3258."

 

字典方法：

清除：clear

 

>>> x = {}

>>> y = x

>>> x['key'] = 'value'

>>> y

{'key': 'value'}

>>> x = {}

>>> y

{'key': 'value'}

And here’s the second scenario:

>>> x = {}

>>> y = x

>>> x['key'] = 'value'

>>> y

{'key': 'value'}

>>> x.clear()

>>> y

{}

 

复制：copy

 

>>> x = {'username': 'admin', 'machines': ['foo', 'bar', 'baz']}

>>> y = x.copy()

>>> y['username'] = 'mlh'

>>> y['machines'].remove('bar')

>>> y

{'username': 'mlh', 'machines': ['foo', 'baz']}

>>> x

{'username': 'admin', 'machines': ['foo', 'baz']}

 

>>> from copy import deepcopy

>>> d = {}

>>> d['names'] = ['Alfred', 'Bertrand']

>>> c = d.copy()

>>> dc = deepcopy(d)

>>> d['names'].append('Clive')

>>> c

{'names': ['Alfred', 'Bertrand', 'Clive']}

>>> dc

{'names': ['Alfred', 'Bertrand']}

 

复制key：fromkeys

>>> {}.fromkeys(['name', 'age'])

{'age': None, 'name': None}

 

>>> dict.fromkeys(['name', 'age'], '(unknown)')

{'age': '(unknown)', 'name': '(unknown)'}

 

获取：

>>> d = {}

>>> print d['name']

Traceback (most recent call last):

File "", line 1, in ?

KeyError: 'name'

>>> print d.get('name')

None

 

>>> d.get('name', 'N/A')

'N/A'

 

是否有key：

列出值：items and iteritems

列出关键字：keys and iterkeys

取值：pop

>>> d = {'x': 1, 'y': 2}

>>> d.pop('x')

1

>>> d

{'y': 2}

出栈：popitem

       但是没有append。

setdefault：设置默认值。

 

更新：update

>>> d = {

'title': 'Python Web Site',

'url': '',

'changed': 'Mar 14 22:09:15 MET 2008'

}

>>> x = {'title': 'Python Language Website'}

>>> d.update(x)

>>> d

{'url': '', 'changed':

'Mar 14 22:09:15 MET 2008', 'title': 'Python Language Website'}

 

 

取值：values and itervalues