Python的dict字典结构操作方法学习笔记
一.字典的基本方法
1.新建字典
1）、建立一个空的字典
>>> dict1={}
>>> dict2=dict()
>>> dict1,dict2
({}, {})
>>> dict1={1:'a',2:'b',3:'c'}
>>> dict1
{1: 'a', 2: 'b', 3: 'c'}
>>> dict1=dict([(1,'a'),(2,'b'),(3,'c')])
>>> dict1
{1: 'a', 2: 'b', 3: 'c'}
2、获取方法
1）、get（key） 从字典中获取一个key对应的value,返回value
>>> dict1={1:'a',2:'b',3:'c'}
>>> dict1.get(1)
'a'
如果字典里面不存在，则返回一个 NoneType
>>> type(dict1.get(4)) <type 'NoneType'>
>>> dict1.get(4,'not found') 'not found'
2）、keys（） 获取字典中所有的key值，返回一个列表
>>> dict1.keys() [1, 2, 3]
3）、values（） 与keys（）方法对应，返回的字典中的所有value的列表
>>> dict1.values() ['a', 'b', 'c']
4）、items（） 返回一个 (key,value)对应的元组
>>> dict1.items() [(1, 'a'), (2, 'b'), (3, 'c')]
5）、iterkeys() , itervalues() , iteritems() 也是分别获取所有的key，value，(key,value)元祖，只是不在是返回列表，而是一个迭代器
>>> for key in dict1.iterkeys(): print key 1 2 3
3、设置字典值的方法
1）、直接的方法就是
>>> dict1[4]='d'
>>> dict1
{1: 'a', 2: 'b', 3: 'c', 4: 'd'}
但是，这个方法就是，如果我想添加的key值已经在字典中，那么就会覆盖掉原来的value值
>>> dict1[4]='e'
>>> dict1
{1: 'a', 2: 'b', 3: 'c', 4: 'e'}
2）、setdefault（key，value） 这个方法的好处就是，如果插入的key不存在字典中，那么插入字典并返回该value，否则的存在于字典中的话，那么返回存在的value，不会覆盖掉
>>> dict1
{1: 'a', 2: 'b', 3: 'c', 4: 'e'}
>>> dict1.setdefault(5,'f')
'f'
>>> dict1.setdefault(5,'g')
'f'
>>> dict1
{1: 'a', 2: 'b', 3: 'c', 4: 'e', 5: 'f'}
4、删除字典
1）pop(key) 删除指定key的一项，成功返回一个删除项的value, 如果不存在，会抛出异常，所以在用这个方法时候，都要用判断 key是否存在，或者catch这个异常
>>> def pop_key(d,key):
try:
d.pop(key)
print "sucess"
except:
print "key is not in dict"
>>> dict1
{1: 'a', 2: 'b'}
>>> pop_key(dict1,3)
key is not in dict
或者
>>> def sub_dict2(d,key): if d.has_key(key): d.pop(key) print "sucess" else:print "key is not in dict" >>> pop_key(dict1,3) key is not in dict
2） popitem() 和pop（）类似，只是他是删除一个（key，value）的元组
利用上面的方法，可以得使用一些进阶的用法
A、我们通过2个列表来创建一个字典，第一个列表是所有的key，第二个列表是所有的value
>>> list1=[1,2,3]
>>> list2=['a','b','c']
>>> dict1=dict(zip(list1,list2))
>>> dict1
{1: 'a', 2: 'b', 3: 'c'}
B、找出某一个字典的子字典
>>> dict1
{1: 'a', 2: 'b', 3: 'c'}
>>> dict1=dict([(1,'a'),(2,'b'),(3,'c')])
>>> dict1
{1: 'a', 2: 'b', 3: 'c'}
>>> subkeys=[1,3]
>>> def sub_dict(d,subkeys):
return dict([(k,d.get(k)) for k in subkeys if k in d])
>>> print sub_dict(dict1,subkeys)
{1: 'a', 3: 'c'}
C、反转字典，也就是key变成新字典的value，value变成新字典的key（注意，如果value值有重复，反转后的字典就只会保留一个
>>> def invert_dict(d):
return dict([(k,v) for v,k in d.iteritems()])
>>> print invert_dict(dict1)
{'a': 1, 'c': 3, 'b': 2}
>>>
1） has_key(key) 判断key是否在字典中
2）copy()返回一个字典的副本（该复制是一个浅复制）
>>> d2={1:[1],2:[2],3:[3]}
>>> d3=d2.copy()
>>> d3[1].append(4)
>>> d2[1]
[1, 4]
如果要深复制的话，就要用到copy.deepcopy(a)
>>> d2={1:[1],2:[2],3:[3]}
>>> import copy
>>> d3=copy.deepcopy(d2)
>>> d3[1].append(4)
>>> print d2[1] , d3[1]
[1] [1, 4]
3）clear( ) 清空dict
4）update(d) 用一个字典来跟新另外一个字典，有点类似与2个字典的合并
>>> dict1={1: 'a', 2: 'b', 3: 'c'}
>>> dict2={1:'x',4:'y'}
>>> dict1.update(dict2)
>>> dict1
{1: 'x', 2: 'b', 3: 'c', 4: 'y'}
>>>
二、遍历
字典的遍历方法很多
1、直接利用dict
>>> d
{'a': 'aa', 'c': 'cc', 'b': 'bb'}
>>> for i in d:
print i,d[i]
a aa
c cc
b bb
2、利用items()
>>> for i,v in d.items(): print i,v a aa c cc b bb
当然也可以这样
>>> for (i,v) in d.items(): print i,v a aa c cc b bb
3、iteritems()
（我觉得比较好的方法）
>>> for k,v in d.iteritems(): print k,v a aa c cc b bb
三、一些进阶用法
1、一键多值
一般情况，字典都是一对一映射的，但如果我们需要一对多的映射，比如一本书，我们要统计一些单词出现的页数。那么，可以用list作为dict的value值。在利用setdefault()方法就可以完成
>>> d={'hello':[1,4,9],"good":[1,3,6]}
>>> d
{'good': [1, 3, 6], 'hello': [1, 4, 9]}
>>> d.setdefault('good',[]).append(7)
>>> d
{'good': [1, 3, 6, 7], 'hello': [1, 4, 9]}
>>> d.setdefault('bad',[]).append(2)
>>> d
{'bad': [2], 'good': [1, 3, 6, 7], 'hello': [1, 4, 9]}
>>>
当然，如果写成一个函数话，就可以更方便的使用，
我们也可以利用set来代替list
>>> def addFunc(d,word,pag):
d.setdefault(word,set()).add(pag)
>>> d={'hello':set([1,4,9]),"good":set([1,3,6])}
>>> addFunc(d,'hello',8)
>>> d
{'good': set([1, 3, 6]), 'hello': set([8, 1, 4, 9])}
>>> addFunc(d,'bad',8)
>>> d
{'bad': set([8]), 'good': set([1, 3, 6]), 'hello': set([8, 1, 4, 9])}
2、利用字典完成简单工厂模式
字典的value不单单只是一些常见的字符串，数值，还可以是类和方法，比如我们就可以这样来实现简单工厂模式
>>> class cat(object):
def __init__(self):
print 'cat init'
>>> class dog(object):
def __init__(self):
print 'dag init'
>>> d={'cat':cat,'dog':dog}
>>> def factoryFunc(d,name):
if name in d:
return d[name]()
else:
raise Exception("error")
>>> cat=factoryFunc(d,'cat')
cat init
>>> def deal_cat():
print 'cat run!!'
>>> def deal_dog():
print 'dag run!!'
>>> d={'cat':deal_cat ,'dog':deal_dog }
>>> animal='cat'
>>> d[animal]()
cat run!!
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