python循环遍历

for循环
append() 方法向列表的尾部添加一个新的元素。
1）循环字符串

str_1='abcde你好呀！'
result=[]
for i in str_1:
    result.append(i)
print(result)

2）循环列表

list_1=['a','b','c','你','好','呀','！']
result=[]
for i in list_1:
    result.append(i)
print(result)

3）循环range

range_1=range(10)
result=[]
for i in range_1:
    result.append(i)
print(result)

4）循环字典

dict_1={'a':1,'b':2,'c':'好'}
result=[]
for i in dict_1:
    result.append(i)
print(result)

5）循环遍历文件

for content in open ('test.txt',encoding='utf-8'):
    print(content)

6）循环1到5相乘

sum = 1
for i in list(range(1,6)):
    sum *= i
print('1*2*3*4*5=',sum)

7）使用len()和range()函数的for循环

name=['li','w','chen']
for i in range(len(name)) :
    print(name[i])
print(len(name))

1.循环遍历对象

1.1vue 在html里面循环遍历对象

v-for=" (val, key , i) in dimItemMap" :key="key"
val-每一项
key -key值
i-第几个

<el-table-column prop="score" label="评分" :show-overflow-tooltip="true" align="center">
            <template slot-scope="scope">
              <span>
                <span v-for=" (val, key , i) in scope.row.dimItemMap" :key="key">
                  {{val.score}}//score为键，val.score为值
                </span>
           </span>
       </template>
</el-table-column>

1.2 在js里面forin遍历对象

for…in 循环主要是为了遍历对象而生，不适用于遍历数组

let data = [{ wiun2dvi: 232, wiun3dvi: 55, wiu4ndvi: 33, wiun1dvi: 24432 }];
    data.forEach((item,index)=>{
      for (const key in item) {
        console.log("item[key]",item[key]);//值
        console.log("key",key);//键
      }
    })

2.循环遍历数组

2.1 vue 在html里面循环遍历数组

<el-table-column v-for="item in tableCol" :key="item.id" :prop="item.id" :label="item.name" :show-overflow-tooltip="true" align="center">
      <template slot-scope="scope">
           <span>{{scope.row.dimItemMap?scope.row.dimItemMap[item.id].name:""}}</span>
      </template>
</el-table-column>

<el-table-column prop="score" label="评分" :show-overflow-tooltip="true" align="center">
            <template slot-scope="scope">
              <span>
                <span v-for=" (item, index) in scope.row.dimItemMap" :key="index">
                  {{item.score}}
                </span>
           </span>
       </template>
</el-table-column>

2.2 在js里面for遍历数组

let id = 1524466
for (let i = 0; i < list.length; i++) {
        let a = list[i];
        if (a.id === id) {
          return a.name;
        } 
}

2.3 在js里面forof遍历数组

           let arr = [{
                name: 12,
                hello: "wsdfnioq",
            }, {
                name: 12,
                hello: "wsdfnioq",
            }, {
                name: 12,
                hello: "wsdfnioq",
            }]
            for (const i of arr) {
                console.log("i", i);
            }
//i {name: 12, hello: 'wsdfnioq'}
// i {name: 12, hello: 'wsdfnioq'}
 //i {name: 12, hello: 'wsdfnioq'}

2.4 forin，不推荐对数组进行遍历

let arr = ["lsadnkol", "klsmvaod", "lpsaojfoas"]
for (const key in arr) {
    console.log("arr", key, typeof key, arr[key]);
}
// 0 string lsadnkol
// 1 string klsmvaod
// 2 string lpsaojfoas

2.4 forEach() 函数遍历数组

①无任何返回，可改变原来数组中的内容
②循环次数：数组的长度
③不支持return，不需要return语句

如下案例：给每个对象中添加age属性

    let forArr = [{name:'tom',sex:'man'},{name:'linda',sex:'woman'},]
     forArr.forEach((item,index) => {
        console.log("forEach循环==index==",index,item);
         item.age = 27
    })

    console.log("forArr==遍历后===",forArr)
   // forArr ---->[{name:'tom',sex:'man',age:27},{name:'linda',sex:'woman',age:27}]

3.循环遍历字符串

3.1for

let s = "abcd"
for (let i = 0; i < s.length; i++) {
      console.log(i, typeof i, s[i]); //i为索引,s[i]为值,typeof i 为number
}
//  0 number a
//  1 number b
//  2 number c
//  3 number d

3.2 forin

let s = "abcd"
for (const key in s) {
    console.log("key", key, typeof key, s[key]); //key为索引,s[key]为值,typeof key 为string
}
// 0 string a
// 1 string b
// 2 string c
// 3 string d

3.3 forof

let s = "abcd"
for (const i of s) {
    console.log("i", i);//i为值
}
// a 
// b 
// c 
// d