python dict用法

鍵（Key）值（Value）對應的物件，鍵物件必須是 hashable。以下是一些操作示範：

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>>> passwords = { 'Justin' : 123456 , 'caterpillar' : 933933 } >>> passwords[ 'Justin' ] 123456 >>> passwords[ 'Hamimi' ] = 970221 # 增加一對鍵值 >>> passwords { 'caterpillar' : 933933 , 'Hamimi' : 970221 , 'Justin' : 123456 } >>> del passwords[ 'caterpillar' ] # 刪除一對鍵值 >>> passwords { 'Hamimi' : 970221 , 'Justin' : 123456 } >>> passwords.items() [( 'Hamimi' , 970221 ),( 'Justin' , 123456 )] >>> passwords.keys() [ 'Hamimi' , 'Justin' ] >>> passwords.values() [ 970221 , 123456 ] >>>

使用

[]

時如果指定的鍵不存在，會發生

KeyError

，可以使用

dict

的

get

方法，指定鍵不存在時傳回的預設值。例如：

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>>> passwords.get( 'openhome' , '000000' ) '000000' >>> passwords[ 'openhome' ] Traceback (most recent call last): File "" ,line 1 ,in KeyError: 'openhome' >>>

#字典的添加、删除、修改操作

dict = {"a" :"apple","b" :"banana","g" :"grape","o" :"orange"}

dict["w"] ="watermelon"

del(dict["a"])

dict["g"] ="grapefruit"

print dict.pop("b") # 会讲原dict里的内容修改， 无需重新赋值

print dict

dict.clear()#全部清空

print dict

#字典的遍历

dict = {"a" :"apple","b" :"banana","g" :"grape","o" :"orange"}

for k in dict:
print "dict[%s] =" % k,dict[k]

#字典items()的使用

dict = {"a" :"apple","b" :"banana","c" :"grape","d" :"orange"}

#每个元素是一个key和value组成的元组，以列表的方式输出

print dict.items()

#调用items()实现字典的遍历

dict = {"a" :"apple","b" :"banana","g" :"grape","o" :"orange"}

for (k,v) in dict.items():
print "dict[%s] =" % k,v

#调用iteritems()实现字典的遍历

dict = {"a" :"apple","b" :"banana","c" :"grape","d" :"orange"}

print dict.iteritems()

for k,v in dict.iteritems():
print "dict[%s] =" % k,v

for (k,v) in zip(dict.iterkeys(),dict.itervalues()):
print "dict[%s] =" % k,v



#使用列表、字典作为字典的值

dict = {"a" :("apple",),"bo" :{"b" :"banana","o" :"orange"},"g" :["grape","grapefruit"]}

print dict["a"]

print dict["a"][0]

print dict["bo"]

print dict["bo"]["o"]

print dict["g"]

print dict["g"][1]



dict = {"a" :"apple","b" :"banana","c" :"grape","d" :"orange"}

#输出key的列表

print dict.keys()

#输出value的列表

print dict.values()

#每个元素是一个key和value组成的元组，以列表的方式输出

print dict.items()

dict = {"a" :"apple","b" :"banana","c" :"grape","d" :"orange"}

it = dict.iteritems()

print it

#字典中元素的获取方法

dict = {"a" :"apple","b" :"banana","c" :"grape","d" :"orange"}

print dict

print dict.get("c","apple")#如果c存在，则取出c对应的value,print dict.get("e","apple")#如果e 不存在，则取出apple对应的key

#get()的等价语句

D = {"key1" :"value1","key2" :"value2"}

if "key1" in D:
print D["key1"]

else:
print "None"

#字典的更新

dict = {"a" :"apple","b" :"banana"}

print dict

dict2 = {"c" :"grape","d" :"orange"}

dict.update(dict2)#讲dict2的内容全部加入dic

print dict

#udpate()的等价语句

D = {"key1" :"value1","key2" :"value2"}

E = {"key3" :"value3","key4" :"value4"}

for k in E:
D[k] =E[k]

print D

#字典E中含有字典D中的key

D = {"key1" :"value1","key2" :"value2"}

E = {"key2" :"value3","key4" :"value4"}

for k in E:
D[k] =E[k]

print D

#设置默认值

dict = {}

dict.setdefault("a")

print dict

dict["a"] ="apple"

dict.setdefault("a","default") #如果已经添加了value,则再用default也不会更改里面的value

print dict

#调用sorted()排序

dict = {"a" :"apple","b" :"grape","c" :"orange","d" :"banana"}

print dict

#按照key排序

print sorted(dict.items(),key=lambda d:d[0])

#按照value排序

print sorted(dict.items(),key=lambda d:d[1])

#字典的浅拷贝

dict = {"a" :"apple","b" :"grape"}

dict2 = {"c" :"orange","d" :"banana"}

dict2 = dict.copy()

print dict2

#字典的深拷贝

import copy

dict = {"a" :"apple","b" :{"g" :"grape","o" :"orange"}}

dict2 = copy.deepcopy(dict)

dict3 = copy.copy(dict)

dict2["b"]["g"] ="orange"

print dict

dict3["b"]["g"] ="orange"# dict3 与dict 指向了同一快地址空间，因此改变dict3 就改变了dict

print dict