4.Python的不堪一击到初学乍练(列表,元组)

Python(列表,元组)

一.列表

1. 列表初识

   • 列表是python的基础数据类型之一,其他编程语言也有类似的数据类型.
     
     比如JS中的数组, java中的数组等等,它是以[ ]括起来, 每个元素用","隔开并且可以存放各种数据类型.
   • 列表相比于字符串,不仅可以存放不同的数据类型,并且可以存放大量的数据.
     
     当32位Python可以存放:536870912个元素, 当64位Python可以存放:1152921504606846975个元素,并且列表是按照你保存的顺序进行排序的,有索引并且可以切片,方便取值.

2. 列表索引,切片和操作

   1.1 列表的索引

   ​ 列表与字符串一样也有索引:

   # 列表索引的应用
   lst = ["asd", "你好", "hell world", 123, "升仙"]
   print(lst[0]) # 获取第一个元素
   print(lst[1]) # 获取第二个元素
   print(lst[2]) # 获取第三个元素
   print(lst[3]) # 获取第四个元素
   print(lst[4]) # 获取第五个元素
   # 列表是可变的与字符串不同这点要注意,在列表的操作中会有说明.
   

   1.2 列表的切片

   ​ 列表与字符串一样可进行切片操作

   lst = ["asd","你好","hell world",123,"升仙"]
   print(lst[0:3]) # ["asd","你好","hell world"]
   print(lst[:3]) # ["asd","你好","hell world"]
   print(lst[1::2]) # ["你好",123] 列表同样有步长
   print(lst[2::-1]) # ["hell world","你好","asd"] 步长位置的正负控制着取值的方向
   print(lst[-1:-4:-2]) # ["升仙","hell world"]
   # 列表和字符串的操作基本类似,因此操作起来并不难举一反三即可.
   

   1.3 列表的操作(增,删,改,查,其他操作)

   注意 : list和str不一样, lst可以发生改变.,所以可以直接在原来list对象上进行操作.

   ​ 1.3.1 列表的增加

   # 在列表后新增
   lst = ["asd","你好","hell world",123,"升仙"]
   print(lst)
   lst.append("wusir")
   print(lst) # ["asd","你好","hell world",123,"升仙","wusir"]
   ---------------------------------
   # 根据索引位置插入
   lst = ["asd","你好","hell world",123,"升仙"]
   lst.insert(1,"成仙") # 在索引为1的位置插入刘德华,原来的元素向后移动一位.
   print(lst) # ["asd","成仙","你好","hell world",123,"升仙"]
   ---------------------------------
   # 迭代添加
   lst = ["asd","你好","hell world",123,"升仙"]
   lst2 = ["升仙成功","升仙失败"]
   lst.extend(lst2)
   print(lst) # ["asd","你好","hell world",123,"升仙","升仙成功","升仙失败"]
   print(lst2) # ["升仙成功","升仙失败"]
   # lst2列表添加到lst列表中,lst2本身不变.
   

   ​ 1.3.2 列表的删除

   ​ 列表的删除有四种方式(pop,remove,clear,del)

   # pop删除用法
   lst = ["asd","你好","hell world",123,"升仙"]
   print(lst)
   el = lst.pop() # 当pop()括号内为空时,默认删除最后一个索引所对应的的数据.
   print(el) # 打印结果:升仙,pop删除列表的某一项时,会有返回值,其返回值就是被pop删除的内容.
   print(lst) # ["asd","你好","hell world",123]
   
   lst = ["asd","你好","hell world",123,"升仙"]
   el2 = lst.pop(2) # 删除索引为2的位置的值
   print(el2) # hell world
   print(lst) # ["asd","你好",123,"升仙"]
   ---------------------------------
   # remove删除用法
   lst = ["asd","你好","hell world",123,"升仙"]
   lst.remove("升仙") # 可以删除指定元素,当删除不存在的元素会报错
   print(lst) # ["asd","你好","hell world",123]
   ---------------------------------
   # clear删除用法
   lst.clear() # 清空list
   print(lst) # []
   ---------------------------------
   # 切片删除
   del lst[1:3] # 强制删除
   print(lst) # ["asd",123,"升仙"]
   

   ​ 1.3.3 列表的修改

   # 列表的修改
   lst = ["asd","你好","hell world",123,"升仙"]
   lst[1] = "飞升" # 把1号元素修改成飞升
   print(lst) # ["asd","飞升","hell world",123,"升仙"]
   lst[:4:2] = ["返璞归真", "融会贯通"] # 切片修改也可以,同时注意当步长不是1时,元素的个数要一一对应额否则会报错
   print(lst) # ["返璞归真","飞升","融会贯通",123,"升仙"]
   lst[1:4] = ["霸气外露"] # 如果切片没有步长或者步长是1时,则不用管替换的个数.
   print(lst) # ["返璞归真","霸气外露","升仙"]
   

   ​ 1.3.4 列表的查询

   ​ 列表是一个可以迭代的对象

   # 用for查询打印列表每一个元素
   lst = ["asd","你好","hell world",123,"升仙"]
   for el in lst:
    print(el)
   ---------------------------------
   # 查询元素在列表中出现的次数
   lst = ["asd","你好","hell world",123,"升仙"]
   c = lst.count("升仙") # 查询升仙出现的次数
   print(c) # 1
   ---------------------------------
   # 查询列表的长度
   lst = ["asd","你好","hell world",123,"升仙"]
   l=len(lst) # 列表的长度,与字符串的使用方式相同
   print(l) # 5
   

   ​ 1.3.4 列表的其他操作

   # 升序
   lst = [1,2,15,23,4,33]
   lst.sort() # 排序,默认为升序.
   print(lst) # [1,2,4,15,23,33]
   ---------------------------------
   # 降序
   lst.sort(reverse=True) # 降序
   print(lst) # [33,23,15,4,2,1]
   ---------------------------------
   # 翻转(倒序)
   lst = ["asd","你好","hell world",123,"升仙"]
   lst.reverse() # 此方法只针对列表内的各个元素,倒序
   print(lst) # ["升仙",123,"hell world","你好","asd"]
   

3. 列表嵌套

   一层一层看灵活运用即可,融会贯通.

   lst = ["武当","峨眉","少林",["崆峒",["极乐谷"],"华山"],"魔教"]
   # 找到峨眉
   print(lst[2])
   # 找到少林和魔教
   print(lst[2:])
   # 找到崆峒
   print(lst[3][0])
   # 将崆峒改成丐帮
   lst[3][0]="丐帮"
   print(lst) # ['武当','峨眉','少林',['丐帮',['极乐谷'],'华山'],'魔教']
   # 在lst列表后添加"丐帮"
   lst.append("丐帮")
   print(lst) # ['武当','峨眉','少林',['崆峒',['极乐谷'],'华山'],'魔教','丐帮']
   

二.元组

1. 元组初识

   ​ 元组俗称不可变的列表,又称为只读列表,元组也是python的基本数据类型之一,用小括号括起来,里面可以放任何数据类型的数据,循环也可以,查询可以,切片也可以,就是不能改.

   ​ 注意: 这里元组的不可变的意思是当子元素是不可变对象时元素不可变,当子元素为可变对象时是可以变的, 这取决于子元素是否是为可变对象.

   ​ 元组中如果只有一个元素,需要添加一个逗号,否则就不是一个元组,当tu=()时,print(type(tu)),打印结果显示tu是元组.

2. 元组嵌套

   ​ 元组也有,len(),count(),index()等方法,可以自己尝试直至融会贯通.

   # 元组取值和切片
   tup = ("asd","你好","hell world",123,"升仙")
   print(tup[0]) # asd
   print(tup[2]) # hell world
   print(tup[2:]) # ("hell world",123,"升仙") 切片后仍然是元组
   ---------------------------------
   # for循环
   tup = ("asd","你好","hell world",123,"升仙")
   for el in tup:
   	print(el)
   ---------------------------------
   # 当元组内的子元素时可变类型时可以进行操作,将武当换成丐帮
   tup = ("asd","你好","hell world",123,["武当","峨眉","少林"])
   tup[-1][0]="丐帮"
   print(tup) # ("asd","你好","hell world",123,["丐帮","峨眉","少林"])
   # 这里元组的不可变的意思是子元素不可变,而字元素内部的子元素是可以变, 这取决于子元素是否是可变对象.