#索引与切片 ##1.序列 序列:list,tuple,str 其中list是可变序列 typle,str是不可变序列 #修改序列的值 list = [3,4,5] tup = (3,4,5) str = '345' list[1] = 99 list
output:[3, 99, 5]
tup[1] = 99 tup
Output:TypeError Traceback (most recent call last) Input In [5], in <cell line: 1>() ----> 1 tup[1] = 99 2 tup TypeError: 'tuple' object does not support item assignment
str[1] = 'y'
str
Output:
TypeError Traceback (most recent call last) Input In [6], in <cell line: 1>() ----> 1 str[1] = 'y' 2 str TypeError: 'str' object does not support item assignment
!!!!此处不是代码错误,纯纯为了演示不可变序列不能修改序列的值
###2.索引 list=[1,2,3,4,5,[1,2,3,4,5]] print(list) print(list[0],list[1]) ###python中的索引是从0开始的,list[0]代表第一个索引,list[1]代表第二个索引 Output: [1, 2, 3, 4, 5, [1, 2, 3, 4, 5]] 1 2 len(list)
Output:2 list=[1,2,3,4,5,[1,2,3,4,5]] print(list) print(list[-1],list[-2]) ###倒数第二个数用list[-1]表示,倒数第二个数用list[-2]表示 Output: [1, 2, 3, 4, 5, [1, 2, 3, 4, 5]] [1, 2, 3, 4, 5] 5 tup=['a','b','c','d'] print(tup[2],tup[-1])
Output:c d #字符串也是索引 str='abcdefg' print(st[0],st[-2]) Output:a f
###3.切片 切片用:表示 切片是一个左闭又开的区间 list=[1,2,3,4,5,[1,2,3,4,5]] print(list[2:3])#索引2到索引3,但不包含索引3 print(list[:2])#索引0到索引2,但不包含索引2 print(list[1:])#索引1到最后一个元素,且包含最后一个元素 print(list[1:-1])#索引1到最后一个元素,但不包括最后一个元素 Output: [3] [1, 2] [2, 3, 4, 5, [1, 2, 3, 4, 5]] [2, 3, 4, 5] tup=['a','b','c','d'] print(tup[1:3]) print(tup[0:]) print(tup[0:3]) Output: ['b', 'c'] ['a', 'b', 'c', 'd'] ['a', 'b', 'c'] str='abcdefg' print(str[0:]) print(str[0:6]) print(str[1:4]) Output: abcdefg abcdef bcd
###4.步长 list=[10,20,30,40,50,60,70,80,90] print(list[::3]) ###list[a:b:n] 对于list序列,从索引a至索引b,但不包含索引b,其中间隔为n(步长) Output: [10, 40, 70]
###列表的常用方法
list=[10,20,30,40,50,60,70,80,90] print(len(list))###长度 Output:9 list.append(99) list.append(['a','b'])####append是可以直接在原数据后边➕列表 print(list) Output: [10, 20, 30, 40, 50, 60, 70, 80, 90, 99, ['a', 'b']] list=[10,20,30,40,50,60,70,80,90] list.extend(['a','b'])###在原数据后方直接追加另一个序列中的多个值 print(list) Output: [10, 20, 30, 40, 50, 60, 70, 80, 90, 'a', 'b'] list=[10,20,30,40,50,60,70,80,90] list.insert(2,1000) print(list) Output: [10, 20, 1000, 30, 40, 50, 60, 70, 80, 90]
标签:Python,list,切片,索引,str,print,Output,tup From: https://www.cnblogs.com/dd0016/p/16716707.html