Python基礎教程之第4章字典: 當索引不好用時

Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32
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#4.1字典的使用
>>> names=['Alice','Beth','Cecil','Dee-Dee','Earl']
>>> numbers=['2341','9102','3158','042','5551']
>>> names=['Alice','Beth','Cecil','Dee-Dee','Earl']
>>> numbers=['2341','9102','3158','042','5551']
>>> numbers[names.index('Cecil')]
'3158'
>>> 0142
98
>>> 0912
SyntaxError: invalid token
>>> 0812
SyntaxError: invalid token
#4.2創建和使用字典
>>> phonebook={'Alice':'2341','Beth':'9102','Cecil':'3258'}
>>> phonebook['Cecil']
'3258'
#4.2.1 dict函數
>>> 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'}
#4.2.2 基本字典操作
#len(d)返回d中項(鍵值對)的數量
#d[k]返回關聯到鍵k上的值
#d[k]=v將值v關聯到鍵k上
#del d[k]刪除鍵爲k的項
#k in d檢查d中是否包含鍵爲k的項
#鍵的類型:字典的鍵可以是整型,浮點型(實型),字符串或元組. 字典的鍵可以是任何不可變類型.
#在字典中檢查鍵的成員資格比在列表中檢查值的成員資格更有效,數據結構的規模越大,兩者的效率差距越明顯
>>> x=[]
>>> x[42]='Foobar'

Traceback (most recent call last):
  File "<pyshell#24>", line 1, in <module>
    x[42]='Foobar'
IndexError: list assignment index out of range
>>> x={}
>>> x[42]='Foobar'
>>> x
{42: 'Foobar'}
#代碼清單4-1 字典示例
#4.2.3 字典的格式化字符串
>>> phonebook
{'Beth': '9102', 'Alice': '2341', 'Cecil': '3258'}
>>> "Cecil's phone number is %(Cecil)s. " % phonebook
"Cecil's phone number is 3258. "
>>> template = '''<html>
	<head><title>%(title)s</title></head>
	<body>
	<h1>%(title)s</h1>
	<p>%(text)s</p>
	</body>'''
>>> data = {'title':'My Home Page', 'text':'Welcome to my home page!'}
>>> print template % data
<html>
	<head><title>My Home Page</title></head>
	<body>
	<h1>My Home Page</h1>
	<p>Welcome to my home page!</p>
	</body>

#4.2.4 字典方法
#1.clear方法
>>> d={}
>>> d['name']='Gumby'
>>> d['age']=42
>>> d
{'age': 42, 'name': 'Gumby'}
>>> returned_value = d.clear()
>>> d
{}
>>> print returned_value
None
>>> x={}
>>> y=x
>>> x['key']='value'
>>> y
{'key': 'value'}
>>> x={}
>>> y
{'key': 'value'}
>>> 
>>> x={}
>>> y=x
>>> x['key']='value'
>>> y
{'key': 'value'}
>>> x.clear()
>>> y
{}
#2.copy方法,這個方法實現的是淺複製(shallow 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']}
#使用深複製(deep copy), 複製一個副本
>>> from copy import deepcopy
>>> d={}
>>> d['names']=''Alfred','Bertrand']
SyntaxError: invalid syntax
>>> d['anmes']=['Afred','Bertrand']
>>> c=d.copy()
>>> c
{'anmes': ['Afred', 'Bertrand']}
>>> d['names']=['Alfred','Bertrand']
>>> d
{'names': ['Alfred', 'Bertrand'], 'anmes': ['Afred', 'Bertrand']}
>>> d.clear()
>>> d['names']=['Alfred','Bertrand']
>>> c=d.copy()
>>> c
{'names': ['Alfred', 'Bertrand']}
>>> dc=deepcopy(d)
>>> d['names'].append('Clive')
>>> c
{'names': ['Alfred', 'Bertrand', 'Clive']}
>>> dc
{'names': ['Alfred', 'Bertrand']}

#3.fromkeys方法
>>> {}.fromkeys(['name','age'])
{'age': None, 'name': None}
>>> dict.fromkeys(['name','age'])
{'age': None, 'name': None}
>>> dict.fromkeys(['name','age'], '(unknown)')
{'age': '(unknown)', 'name': '(unknown)'}
>>> 

#4.get方法
>>> d={}
>>> print d['name']

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    print d['name']
KeyError: 'name'
>>> print d.get['name']

Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    print d.get['name']
TypeError: 'builtin_function_or_method' object has no attribute '__getitem__'
>>> print d.get('name')
None
>>> d.get('name','N/A')
'N/A'
>>> d['name']='Eric'
>>> d.get('name')
'Eric'
#代碼清單4-2 字典方法示例

#5.has_key方法
>>> d={}
>>> d.has_key('name')
False
>>> d['name']='Eric'
>>> d.has_key('name')
True
#6.items和iteritems
>>> d={'title':'Python Web Site', 'url':'http://www.python.org', 'spam':0}
>>> d.items()
[('url', 'http://www.python.org'), ('spam', 0), ('title', 'Python Web Site')]
>>> it = d.iteritems()
>>> it
<dictionary-itemiterator object at 0x0134AF30>
>>> list(it) #Convert the iterator to a list
[('url', 'http://www.python.org'), ('spam', 0), ('title', 'Python Web Site')]
#7.keys方法和iterkeys方法
#keys方法將字典中的鍵以列表形式返回,而iterkeys則返回鍵的迭代器
#8.pop方法
>>> d = {'x':1, 'y':2}
>>> d.pop('x')
1
>>> d
{'y': 2}
>>> 

#9.popitem方法
>>> d={'url':'http://www.python.org', 'spam':0, 'title':'Python Web Site'}
>>> d
{'url': 'http://www.python.org', 'title': 'Python Web Site', 'spam': 0}
>>> d.popitem()
('url', 'http://www.python.org')
>>> d
{'title': 'Python Web Site', 'spam': 0}
>>> d={}
>>> d.setdefault('name', 'N/A')
'N/A'
>>> d
{'name': 'N/A'}
>>> d['name']='Gumby'
>>> d.setdefault('name','N/A')
'Gumby'
>>> d
{'name': 'Gumby'}
>>> d={}
>>> print d.setdefault('name')
None
>>> d
{'name': None}

#11.update方法
>>> d={
	'title':'Python Web Site',
	'url':'http://www.python.org',
	'changed':'Mar 14 22:09:15 MET 2008'
	}
>>> x={'title':'Python Language Website'}
>>> d.update(x)
>>> d
{'url': 'http://www.python.org', 'changed': 'Mar 14 22:09:15 MET 2008', 'title': 'Python Language Website'}

#12. values方法和itervalues方法
>>> d={}
>>> 
>>> d[1]=1
>>> d[2]=2
>>> d[3]=3
>>> d[4]=1
>>> d.values()
[1, 2, 3, 1]
>>> 
#4.3 小結
#映射:映射可以使用任何不可變對象標識元素. 最常用的類型是字符串和元組. Python唯一內建的映射類型是字典.
#利用字典格式化字符串
#字典的方法
#4.3.1本章的新函數
#dict(seq) 用(鍵,值)對(或者映射和關鍵字參數)建立字典

字典示例

#coding=utf-8
#e4-1.py 字典示例
#簡單數據庫
#使用人名作爲鍵的字典,每個人用另一個字典來表示,其鍵'phone'和'addr'分別表示他們的電話號碼和地址.
people = {
	'Alice': {
		'phone':'2341',
		'addr':'Foo drive 23'
	},
	
	'Beth': {
		'phone':'9102',
		'addr':'Bar  street 42'
	},
	
	'Cecil':{
		'phone':'3158',
		'addr':'Baz avenue 90'
	}
}
#針對電話號碼和地址使用的描述性標籤, 會在打印輸出的時候用到
labels = {
	'phone':'phone number',
	'addr':'address'
}

name=raw_input('Name: ')

#查找電話號碼還是地址? 使用正確的鍵:
request = raw_input('Phone number (p) or address (a)? ')

#使用正確的鍵:
if request == 'p': key = 'phone'
if request == 'a': key = 'addr'

#如果名字是字典中的有效鍵纔打印信息:
if name in people: print "%s's %s is %s. " % \
	(name, labels[key], people[name][key])
	
#python e4-1.py
#Name: Beth
#Phone number (p) or address (a)? p
#Beth's phone number is 9102.

字典方法示例

#coding=utf-8
#e4-2
#使用get()的簡單數據庫
#這裏添加代碼清單4-1中插入數據庫的代碼
people = {
	'Alice': {
		'phone':'2341',
		'addr':'Foo drive 23'
	},
	
	'Beth': {
		'phone':'9102',
		'addr':'Bar  street 42'
	},
	
	'Cecil':{
		'phone':'3158',
		'addr':'Baz avenue 90'
	}
}

labels = {
	'phone':'phone number',
	'addr':'address'
}

name = raw_input('Name: ')

#查找電話號碼還是地址?
request = raw_input('Phone number (p) or address(a)? ')

#使用正確的鍵
key = request #如果請求既不是'p'也不是'a'
if request == 'p' : key = 'phone'
if request == 'a' : key = 'addr'

#使用get()提供默認值:
person = people.get(name, {})
label = labels.get(key ,key)
result = person.get(key, 'not available')

print "%s's %s is %s. " % (name, label, result)

#python e4-2.py
#Name: Beth
#Phone number (p) or address(a)? a
#Beth's address is Bar  street 42.

#python e4-2.py
#Name: Cecil
#Phone number (p) or address(a)? p
#Cecil's phone number is 3158.

#python e4-2.py
#Name: Cecil
#Phone number (p) or address(a)? x
#Cecil's x is not available.

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Python基礎教程之第4章 字典: 當索引不好用時

Python基礎教程之第4章字典: 當索引不好用時