Python基础刻意练习——Day12:else 与 with 语句

痛定思痛。 2023-06-10 10:25 30阅读 0赞

[Day1:变量、运算符与数据类型][Day1]  
[Day2:条件与循环][Day2]  
[Day3&4:列表与元组][Day3_4]  
[Day5:字符串与序列][Day5]  
[Day6&7:函数与Lambda表达式][Day6_7_Lambda]  
[Day8:字典与集合][Day8]  
[Day9&10:文件与文件系统][Day9_10]  
[Day11:异常处理][Day11]  
Day12:else 与 with 语句——>本文  
[Day13&14:类与对象][Day13_14]  
[Day15&16:魔法方法][Day15_16]  
[Day17:模块][Day17]

# 一.else语句 #

## 1. if…else… ##

详见[Day2:条件与循环][Day2]，略

## 2.while…else… ##

放在循环外面，若循环顺利结束则执行（break跳出则不执行）

def MaxFactor(num):
        count=num//2
        while count>1:
            if num%count==0:
                print('%d的最大约数是:%d'%(num,count))
                break
            count-=1
        else:
            print('%d是素数'%num)
    num=int(input('请输入一个数:'))
    MaxFactor(num)
    ''' 请输入一个数:17 17是素数 '''

*  for…else…同理

## 3.try…except…else… ##

[Day11:异常处理][Day11]中已说过，略

# 二、with语句 #

with 语句可抽象出文件操作中频繁使用的try、except、finally相关的细节，自动检查是否关闭文件  
减少代码量

try:
        with open(r'data.txt','r+') as f:
            for line in f:
                print(line,end=' ')
    except OSError as e:
        print('出错',e)
    #出错 [Errno 2] No such file or directory: 'data.txt'

p.s.  
上述代码中f是一个TextIOWrapper类  
需通过for语句输出其文本内容  
data.txt内容如下：

python
    data

try:
        with open(r'practise/data.txt','r+') as f:
            print(type(f))
            for line in f:
                print(line,end=' ')
    except OSError as e:
        print('出错',e)
    ''' <class '_io.TextIOWrapper'> python data '''

[Day1]: https://blog.csdn.net/nanashi_F/article/details/102576036
[Day2]: https://blog.csdn.net/nanashi_F/article/details/102576205
[Day3_4]: https://blog.csdn.net/nanashi_F/article/details/102576336
[Day5]: https://blog.csdn.net/nanashi_F/article/details/102576606
[Day6_7_Lambda]: https://blog.csdn.net/nanashi_F/article/details/102728193
[Day8]: https://blog.csdn.net/nanashi_F/article/details/102738525
[Day9_10]: https://blog.csdn.net/nanashi_F/article/details/102746726
[Day11]: https://blog.csdn.net/nanashi_F/article/details/102788316
[Day13_14]: https://blog.csdn.net/nanashi_F/article/details/102827027
[Day15_16]: https://blog.csdn.net/nanashi_F/article/details/102870209
[Day17]: https://blog.csdn.net/nanashi_F/article/details/102873502