Python 列表list使用介绍
一组有序项目的集合 可变的数据类型【可进行增删改查】 列表中可以包含任何数据类型，也可包含另一个列表【可任意组合嵌套】 列表是以方括号“[]”包围的数据集合，不同成员以“,”分隔 列表可通过序号访问其中成员
定义
>>>l=[]#空列表
>>>l=[1,2,3]
>>>l=[1,2,3,['a','b']]
>>>l=list('linuxeye')
>>>l
['l','i','n','u','x','e','y','e']
>>>l=list(range(5))
>>>l
[0,1,2,3,4]
>>>l='1;2;3;4;5'.split(';')
>>>l
['1','2','3','4','5']
内建函数list(a_sequence)可以将一个序列转为列表
索引
正索引是编号是从左到右，0开始；负索引编号是从右往左，-1、-2…；取范围值都是从左至右
>>>LanguageList=['Python','Shell','Perl','PHP','java','C',"C++","Lisp"] >>>LanguageList[0]#取第一个值 'Python' >>>LanguageList[3]#第四个值 'PHP' >>>LanguageList[3:] ['PHP','java','C','C++','Lisp'] >>>LanguageList[:3] ['Python','Shell','Perl'] >>>LanguageList[2:5] ['Perl','PHP','java']
>>>LanguageList[-1]#倒数第一个值 'Lisp' >>>LanguageList[-2]#倒数第二个值 'C++' >>>LanguageList[-5:] ['PHP','java','C','C++','Lisp'] >>>LanguageList[-5:-2] ['PHP','java','C'] >>>LanguageList[:-2] ['Python','Shell','Perl','PHP','java','C']
增加元素
>>>LanguageList
['Python','Shell','Perl','PHP','java','C','C++','Lisp']
>>>LanguageList.append('GO')
>>>LanguageList
['Python','Shell','Perl','PHP','java','C','C++','Lisp','GO']
>>>LanguageList.insert(3,'Python')#往PHP元素前插入
>>>LanguageList
['Python','Shell','Perl','Python','PHP','java','C','C++','Lisp','GO']
>>>LanguageList.extend(['Ruby','C#'])
>>>LanguageList
['Python','Shell','Perl','Python','PHP','java','C','C++','Lisp','GO','Ruby','C#']
搜索
>>>LanguageList=['Python','Shell','Perl','Python','PHP','java','C','C++','Lisp','GO','Ruby','C#']
>>>LanguageList.index('Python')
0
>>>LanguageList.index('C')
6
>>>LanguageList.index('c')
Traceback(mostrecentcalllast):
File"<stdin>",line1,in<module>
ValueError:list.index(x):xnotinlist
>>>'c'inLanguageList
False
>>>LanguageList.index('Python')#统计一个元素的出现次数
2
删除元素
>>>LanguageList=['Python','Shell','Perl','Python','PHP','java','C','C++','Lisp','GO','Ruby','C#']
>>>LanguageList.remove('C')
>>>LanguageList.remove('Python')
>>>LanguageList.remove('c')
Traceback(mostrecentcalllast):
File"<stdin>",line1,in<module>
ValueError:list.remove(x):xnotinlist
>>>LanguageList.pop()
'C#'
>>>LanguageList
['Shell','Perl','Python','PHP','java','C++','Lisp','GO','Ruby']
>>>LanguageList.pop(-2)
['Shell','Perl','Python','PHP','java','C++','Lisp','Ruby']
>>>delLanguageList[-3:-1]
>>>LanguageList
['Shell','Perl','Python','PHP','java','Ruby']
remove从列表中只删除一个值的首次出现。
pop会做两件事:删除列表的最后一个元素,然后返回删除元素的值。
修改元素
>>>LanguageList=['Python','Shell','Perl','Python','PHP','java','Ruby']
>>>LanguageList[-2]='C'
>>>LanguageList
['Python','Shell','Perl','Python','PHP','C','Ruby']
>>>LanguageList[LanguageList.index('C')]='JAVA'
>>>LanguageList
['Python','Shell','Perl','Python','PHP','JAVA','Ruby']
运算符
>>>LanguageList ['Shell','Perl','Python','PHP','java','C++','Lisp','GO','Ruby'] >>>LanguageList=LanguageList+['Python','C'] >>>LanguageList ['Shell','Perl','Python','PHP','java','C++','Lisp','GO','Ruby','Python','C'] >>>LanguageList+=['java'] >>>LanguageList ['Shell','Perl','Python','PHP','java','C++','Lisp','GO','Ruby','Python','C','java'] >>>NumList=[1,2,3]*3 >>>NumList [1,2,3,1,2,3,1,2,3]
排序
>>>NumList=[2,5,3,6,1,4] >>>NumList.reverse() >>>NumList [4,1,6,3,5,2] >>>NumList[::-1]#和reverse效果相同 >>>NumList [2,5,3,6,1,4] >>>NumList.sort() >>>NumList [1,2,3,4,5,6]
sort可接受参数
cmp，比较函数，接受两个参数,小于时返回负，大于返回正，相等返回0 key，指定排序键 reverse，指定是否反序
列表的比较操作,隐式调用cmp方法,比较规则是逐个扫描元素进行比较,如果可以比较,则比较,如果相等扫描下一个元素,如果不相等返回结果,如果两个元素类型不可以比较,就比较两个对象的id()值。如果一直相等,直到一个列表扫描结束,那么返回较长的列表较大
>>>L=[(13,54),(11,59),(15,55),(12,57),(10,56)] >>>L.sort(key=lambdax:x[1]) >>>L [(13,54),(15,55),(10,56),(12,57),(11,59)] >>>L.sort(key=lambdax:x[1],reverse=1)#或者reverse=True >>>L [(11,59),(12,57),(10,56),(15,55),(13,54)]
sort与sorted函数区别
NumList=[2,5,3,6,1,4] >>>sorted(NumList) [1,2,3,4,5,6] >>>NumList [2,5,3,6,1,4] >>>NumList.sort() >>>NumList [1,2,3,4,5,6]
sort:在原list上排序，不返回排序后的list
sorted:不改变原list，返回排序后的list