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Thinking in Python: Difference between str and repr in Python

2023-03-02 10:57:17 时间

### Thinking in Python: Difference between \_\_str\_\_ and \_\_repr\_\_ in Python ###

*   *  区别
     *  网友的一些回答

## 区别 ##

**repr** 和 **str** 的区别在于，后者是在 str() 函数被使用，或是在用 print 函数  
打印一个对象的时候才被调用的，并且它返回的字符串对终端用户更友好。  
如果你只想实现这两个特殊方法中的一个，**repr** 是更好的选择，因为如果一个对象  
没有 **str** 函数，而 Python 又需要调用它的时候，解释器会用 **repr** 作为替代。

## 网友的一些回答 ##

trthhrtz:  
**repr** is used everywhere, except by print and str when a \_\_str\_\_is defined

Alex Martelli:

Unless you specifically act to ensure otherwise, most classes don’t have helpful results for either:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70]  
As you see – no difference, and no info beyond the class and object’s id. If you only override one of the two…:

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70 1]  
as you see, if you override **repr**, that’s ALSO used for **str**, but not vice versa.

Other crucial tidbits to know: **str** on a built-on container uses the **repr**, NOT the **str**, for the items it contains. And, despite the words on the subject found in typical docs, hardly anybody bothers making the **repr** of objects be a string that eval may use to build an equal object (it’s just too hard, AND not knowing how the relevant module was actually imported makes it actually flat out impossible).

So, my advice: focus on making **str** reasonably human-readable, and **repr** as unambiguous as you possibly can, even if that interferes with the fuzzy unattainable goal of making **repr**’s returned value acceptable as input to **eval**!

Mickey Perlstein:  
str is like toString. created so you can print the data repr is like serialize, or pickle. How do i recreate this object if i need to do so using eval()

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70 2]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70]: /images/20220325/af8ca7a3186744c897be207f6a21d470.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70 1]: /images/20220325/dadd3ff3ca654ec9a4f36b69c480445a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1NveVNhdWNlX2xt_size_16_color_FFFFFF_t_70 2]: /images/20220325/e86493d96eaa485f8da80f76d852a8a7.png

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