Скачать или смотреть How to Pretty Print Python Dictionaries with Custom Object Representations

Discover an effective method to `pretty print` Python dictionaries while ensuring that custom objects use their `__str__` representation instead of `__repr__`.
---
This video is based on the question https://stackoverflow.com/q/63012040/ asked by the user 'd34n' ( https://stackoverflow.com/u/13292382/ ) and on the answer https://stackoverflow.com/a/63013540/ provided by the user 'Serge Ballesta' ( https://stackoverflow.com/u/3545273/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Pretty print Python dict

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Pretty Print Python Dictionaries with Custom Object Representations

When working with Python, printing complex structures like dictionaries and lists can sometimes be challenging, especially if they contain custom objects. If you're familiar with the pprint module, you might know that it provides a way to pretty-print Python's built-in container objects. However, you may encounter issues when the default object representation method (__repr__) is called instead of the intended string representation (__str__) for the contained objects.

In this guide, we'll explore an effective solution to this problem by allowing you to dynamically change the representation of class methods to achieve the desired output when pretty-printing your dictionaries.

The Problem at Hand

Consider the following example with a custom class H that contains two methods for string representation:

[[See Video to Reveal this Text or Code Snippet]]

When you create a dictionary d that includes instances of H, and attempt to pretty print this dictionary using the pprint module, you'll notice that it defaults to using __repr__:

[[See Video to Reveal this Text or Code Snippet]]

Current Output

The output looks like this:

[[See Video to Reveal this Text or Code Snippet]]

As you can see, the _repr_ method is called, resulting in the undesired output. Ideally, you would want your dictionary output to reflect the _str_ representations of the H instances:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To fix this issue, you can temporarily override the _repr_ method of your class with the _str_ method specifically for the duration of your pretty printing. Here’s how to do it:

Step-by-Step Implementation

Create a Helper Function: Define a function that will handle the string representation temporarily.

Backup the Original _repr_ Method: Store a copy of the original _repr_ method.

Override _repr__: Set __repr_ to __str__.

Use pprint: Pretty print the dictionary with the modified representation.

Restore the Original __repr__: After printing, restore the original __repr__.

Here’s the complete code with these steps:

[[See Video to Reveal this Text or Code Snippet]]

Expected Output

Using this approach, you will get the following anticipated output:

[[See Video to Reveal this Text or Code Snippet]]

Important Considerations

While this solution is effective and straightforward, it’s essential to be cautious:

Global Changes: The temporary change to the _repr_ method affects the class globally. If you are working in a multithreaded application or using interruption handlers, this could lead to unexpected behaviors.

Scope of Changes: Ensure that you only use this approach when necessary to avoid unexpected side effects in other parts of your code.

In conclusion, this method provides a simple yet powerful way to control how your dictionaries and their contained objects are represented during pretty printing. With proper care, you can use this technique to improve the readability of your outputs involving custom class instances.

Happy coding!