python字典

#######字典dict######## 1. 为什么需要字典类型? >>> list1 = ["name", "age", "gender"] >>> list2 = ["fentiao", 5, "male"] >>> zip(list1, list2)        //通过zip内置函数将两个列表结合,help(zip) [('name', 'fentiao'), ('age', 5), ('gender', 'male')] >>> list2[0]                //在直接编程时,并不能理解第一个索引表示姓名 'fentiao' >>> list2[name] Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: list indices must be integers, not str 故字典是python中唯一的映射类型,key-value(哈希表),字典对象是可变的,但key必须用不可变对象。 2.字典的定义 In [8]: dic = {"name":"linux","age":22}    #######定义一个字典 In [10]: dic["name"]     //根据key找出value值，不能通过索引寻找value值 Out[10]: 'linux' In [11]: dic["age"] Out[11]: 22 In [12]: user = ['westos','linux']   ##########定义列表 In [13]: passwd=['redhat','blue'] In [14]: zip(user,passwd)    //通过zip内置函数将两个列表结合,help(zip Out[14]: [('westos', 'redhat'), ('linux', 'blue')] """""" """""" In [15]: dic={'westos':'redhat','linux':'blue'} In [16]: dic['westos']   //根据key找出value值 Out[16]: 'redhat' In [17]: dic['westos'] =='redhat'   判断key对应的value值字典中知否存在？存在返回Ture

Out[17]: True

3. 字典的添加: In [18]: dic={'westos':'redhat','linux':'blue'} In [19]: dic['xiaobai']='123'   ####key值和value值都不一样，整个添加。 In [20]: dic Out[20]: {'linux': 'blue', 'westos': 'redhat', 'xiaobai': '123'} In [21]: dic['linux']='block'  ########key值一样和value值都不一样；将key对应的value值更新。 In [22]: dic

Out[22]: {'linux': 'block', 'westos': 'redhat', 'xiaobai': '123'}

4. 字典的常用命令 In [23]: dic={'westos':'redhat'} In [24]: dic1={'linux':'blue'} In [25]: dic. dic.clear       dic.items       dic.pop         dic.viewitems dic.copy        dic.iteritems   dic.popitem     dic.viewkeys dic.fromkeys    dic.iterkeys    dic.setdefault  dic.viewvalues dic.get         dic.itervalues  dic.update       dic.has_key     dic.keys        dic.values       In [25]: dic.update(dic1)#######添加更新，####key值和value值都不一样，整个添加 In [26]: dic Out[26]: {'linux': 'blue', 'westos': 'redhat'} In [27]: dic={'westos':'redhat'} In [28]: dic1={'westos':'blue'} In [29]: dic.update(dic1) #### ##key值一样value值不一样；将key对应的value值更新 In [30]: dic

Out[30]: {'westos': 'blue'}

因为字典是无序的，所以没有索引和切片。 In [31]: dic={'westos':'redhat','linux':'blue'} In [32]: dic.pop('westos')   #####删除,必须加key值; Out[32]: 'redhat'                   #####弹出字典中key值为"westos"的元素并返回该key的元素 In [33]: dic Out[33]: {'linux': 'blue'} In [35]: dic={'westos':'redhat','linux':'blue'} In [36]: dic.popitem()         #####删除,不加key值，随机删除 Out[36]: ('westos', 'redhat') In [37]: dic Out[37]: {'linux': 'blue'} In [38]: dic.popitem() Out[38]: ('linux', 'blue') In [39]: dic Out[39]: {} In [40]: dic.popitem()         ####key值删除完了，再删会报错 --------------------------------------------------------------------------- KeyError                                  Traceback (most recent call last) <ipython-input-40-b472158de449> in <module>() ----> 1 dic.popitem()

KeyError: 'popitem(): dictionary is empty'

  >>> dic.clear()                //删除字典的所有元素 >>> dic >>> del dic                      //删除整个字典 >>> dic Traceback (most recent call last):   File "<stdin>", line 1, in <module> NameError: name 'dic' is not defined ########################################################## In [47]: dic={'westos':'redhat','linux':'blue'} In [48]: dic.values()           ##显示value值 Out[48]: ['redhat', 'blue'] In [49]: dic.keys()               ##显示key值 Out[49]: ['westos', 'linux'] In [50]: dic.get("westos")  ##查看key值对应的value值（有） Out[50]: 'redhat' In [51]: dic.get("hello")       ##查看key值对应的value值（没有的情况下，返回值为none） In [52]: print dic.get("hello") None In [53]: dic.has_key("hello")    ##查看key值存在否？不存在显示False Out[53]: False In [54]: dic.has_key("linux")    ##查看key值存在否？存在显示 True

Out[54]: True

>> ddict = {}.fromkeys(('username','password'),'fentiao')         //字典中的key有相同的value值,默认为None >>> ddict {'username': 'fentiao', 'password': 'fentiao'} >>> ddict = {}.fromkeys(('username','password'),) >>> ddict {'username': None, 'password': None}   5.字典的去重功能 In [57]: dic.fromkeys('westos') Out[57]: {'e': None, 'o': None, 's': None, 't': None, 'w': None} In [58]: dic.fromkeys('westos','hello') Out[58]: {'e': 'hello', 'o': 'hello', 's': 'hello', 't': 'hello', 'w': 'hello'} In [59]: dic = {'westos':'redhat','westos':'234'} In [60]: dic

Out[60]: {'westos': '234'}

6.访问字典的值:直接通过key访问,循环遍历字典的遍历

In [76]: dic = {1:'a',2:'2'} In [78]: for key in dic.keys():    ## 建立函数dic.keys()    ....:     print "key=%s" % key    ....:      key=1 key=2 In [79]: for value in dic.values():## 建立函数 dic.values()    ....:     print "value=%s" % value    ....:      value=a value=2 In [81]: for key, value in dic.keys(), dic.values():##### 建立dic.keys()和 dic.values()函数     print "%s -> %s" %(key,value)           ....:      1 -> 2 a -> 2 In [83]: dic.items() Out[83]: [(1, 'a'), (2, '2')] In [86]: for k,v in dic.items():     print "%s = %s" %(k,v)    ....:      1 = a 2 = 2 7. 嵌套赋值

eg1： 对列表li = [34,45,32,132,43,55,]，排序，去除最大值,最小值，求平均值。 In [106]: li = [34,45,32,132,43,55,] In [107]: li.sort() In [108]: li Out[108]: [32, 34, 43, 45, 55, 132] In [109]: li.pop(0) Out[109]: 32 In [110]: li.pop(len(li)-1) Out[110]: 132 In [111]: li Out[111]: [34, 43, 45, 55] In [112]: sum(li)/len(li) Out[112]: 44 eg2:

四则运算： from __future__ import division number1 = input("num1=") operate = raw_input("operate=") number2 = input("num2=") dic ={"+":number1+number2,"-":number1-number2,"*":number1*number2,"/":number1/number2} if operate in dic.keys():     print dic[operate]