Python基础教程之第4章字典: 当索引不好用时

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Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32Type "copyright", "credits" or "license()" for more information.#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'>>> 014298>>> 0912SyntaxError: invalid token>>> 0812SyntaxError: invalid token#4.2创建和使用字典>>> phonebook={'Alice':'2341','Beth':'9102','Cecil':'3258'}>>> phonebook['Cecil']'3258'#4.2.1 dict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'}#4.2.2 基本字典操作#len(d)返回d中项(键值对)的数量#d[k]返回关联到键k上的值#d[k]=v将值v关联到键k上#del d[k]删除键为k的项#k in d检查d中是否包含键为k的项#键的类型:字典的键可以是整型,浮点型(实型),字符串或元组. 字典的键可以是任何不可变类型.#在字典中检查键的成员资格比在列表中检查值的成员资格更有效,数据结构的规模越大,两者的效率差距越明显>>> 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'}#代码清单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_valueNone>>> 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,这个方法实现的是浅复制(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']}#使用深复制(deep copy), 复制一个副本>>> 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'#代码清单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方法将字典中的键以列表形式返回,而iterkeys则返回键的迭代器#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 小结#映射:映射可以使用任何不可变对象标识元素. 最常用的类型是字符串和元组. Python唯一内建的映射类型是字典.#利用字典格式化字符串#字典的方法#4.3.1本章的新函数#dict(seq) 用(键,值)对(或者映射和关键字参数)建立字典

字典示例

#coding=utf-8#e4-1.py 字典示例#简单数据库#使用人名作为键的字典,每个人用另一个字典来表示,其键'phone'和'addr'分别表示他们的电话号码和地址.people = {'Alice': {'phone':'2341','addr':'Foo drive 23'},'Beth': {'phone':'9102','addr':'Bar  street 42'},'Cecil':{'phone':'3158','addr':'Baz avenue 90'}}#针对电话号码和地址使用的描述性标签, 会在打印输出的时候用到labels = {'phone':'phone number','addr':'address'}name=raw_input('Name: ')#查找电话号码还是地址? 使用正确的键:request = raw_input('Phone number (p) or address (a)? ')#使用正确的键:if request == 'p': key = 'phone'if request == 'a': key = 'addr'#如果名字是字典中的有效键才打印信息: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()的简单数据库#这里添加代码清单4-1中插入数据库的代码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: ')#查找电话号码还是地址?request = raw_input('Phone number (p) or address(a)? ')#使用正确的键key = request #如果请求既不是'p'也不是'a'if request == 'p' : key = 'phone'if request == 'a' : key = 'addr'#使用get()提供默认值: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基础教程之第4章 字典: 当索引不好用时

Python基础教程之第4章字典: 当索引不好用时