代码这样写更优雅(Python 版)

素颜马尾好姑娘i 2022-05-27 12:00 229阅读 0赞

Python 这门语言最大的优点之一就是语法简洁，好的代码就像伪代码一样，干净、整洁、一目了然。但有时候我们写代码，特别是 Python 初学者，往往还是按照其它语言的思维习惯来写，那样的写法不仅运行速度慢，代码读起来也费尽，给人一种拖泥带水的感觉，过段时间连自己也读不懂。

《计算机程序的构造和解释》的作者哈尔·阿伯尔森曾这样说：“Programs must be written for people to read, and only incidentally for machines to execute.”

要写出 Pythonic（优雅的、地道的、整洁的）代码，还要平时多观察那些大牛代码，Github 上有很多非常优秀的源代码值得阅读，比如：requests、flask、tornado，笔者列举一些常见的 Pythonic 写法，希望能给你带来一点启迪。

### 1、变量交换 ###

大部分编程语言中交换两个变量的值时，不得不引入一个临时变量：

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### 2、循环遍历区间元素 ###

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xrange 返回的是生成器对象，生成器比列表更加节省内存，不过需要注意的是 xrange 是 python2 中的写法，python3 只有 range 方法，特点和 xrange 是一样的。

### 3、带有索引位置的集合遍历 ###

遍历集合时如果需要使用到集合的索引位置时，直接对集合迭代是没有索引信息的，普通的方式使用：

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### 4、字符串连接 ###

字符串连接时，普通的方式可以用 `+` 操作

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join 是一种更加高效的字符串连接方式，使用 `+` 操作时，每执行一次`+`操作就会导致在内存中生成一个新的字符串对象，遍历8次有8个字符串生成，造成无谓的内存浪费。而用 join 方法整个过程只会产生一个字符串对象。

### 5、打开/关闭文件 ###

执行文件操作时，最后一定不能忘记的操作是关闭文件，即使报错了也要 close。普通的方式是在 finnally 块中显示的调用 close 方法。

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使用 with 语句，系统会在执行完文件操作后自动关闭文件对象。

### 6、列表推导式 ###

能够用一行代码简明扼要地解决问题时，绝不要用两行，比如

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与之类似的还有生成器表达式、字典推导式，都是很 pythonic 的写法。

### 7、善用装饰器 ###

装饰器可以把与业务逻辑无关的代码抽离出来，让代码保持干净清爽，而且装饰器还能被多个地方重复利用。比如一个爬虫网页的函数，如果该 URL 曾经被爬过就直接从缓存中获取，否则爬下来之后加入到缓存，防止后续重复爬取。

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      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(221,17,68);">"http://www.jobbole.com/members/jjq153287083"</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">&gt;</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">@</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,45,122);">cache</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">&lt;</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">/</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,45,122);">a</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">&gt;</span> 
     </div> 
     <div style="border:none;margin:0px;padding:0px 5px;font-family:inherit;background:none;height:inherit;"> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;font-weight:bold;">def</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);"> </span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:#008080;">web_lookup</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">(</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,45,122);">url</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">)</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">:</span> 
     </div> 
     <div style="border:none;margin:0px;padding:0px 5px;font-family:inherit;background:none;height:inherit;"> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;font-weight:bold;">return</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,111,224);"> </span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:#008080;">urllib</span> 
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      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:#008080;">urlopen</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">(</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(0,45,122);">url</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">)</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">.</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:#008080;">read</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">(</span> 
      <span style="border:0px;margin:0px;padding:0px;font-family:inherit;height:inherit;color:rgb(51,51,51);">)</span> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

用装饰器写代码表面上感觉代码量更多，但是它把缓存相关的逻辑抽离出来了，可以给更多的函数调用，这样总的代码量就会少很多，而且业务方法看起来简洁了。

### 8、合理使用列表 ###

列表对象（list）是一个查询效率高于更新操作的数据结构，比如删除一个元素和插入一个元素时执行效率就非常低，因为还要对剩下的元素进行移动

Python

pythonic

Python

deque 是一个双向队列的数据结构，删除元素和插入元素会很快

### 9、序列解包 ###

Python

pythonic

Python

### 10、遍历字典的 key 和 value ###