Скачать или смотреть Understanding the AttributeError in Python Dataclasses: The Misnamed __post_init__

Discover the common mistake of misnaming `__post_init__` in Python dataclasses and learn how to solve the `AttributeError` that arises from it.
---
This video is based on the question https://stackoverflow.com/q/63172560/ asked by the user 'Dariusz Krynicki' ( https://stackoverflow.com/u/4450090/ ) and on the answer https://stackoverflow.com/a/63172677/ provided by the user 'ilmarinen' ( https://stackoverflow.com/u/1024114/ ) 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: python dataclass no attribute post_init

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.
---
Understanding the AttributeError in Python Dataclasses: The Misnamed _post_init_

When working with Python's dataclasses, you might encounter an AttributeError that can leave you scratching your head. Let’s explore a recent dilemma faced by a developer involving the misnaming of the _post_init_ method in a dataclass.

The Problem: AttributeError in Dataclasses

In the provided code, the developer attempts to create a simple dataclass that initializes a dataframe attribute and then sets an additional attribute in the _post_init_ method. However, upon invoking the dataclass, an unexpected AttributeError occurs, indicating that the object has no attribute b.

Code Example with the Error

Here’s the code that led to the problem:

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

The Error Message

When the above code is executed, it results in the following error message:

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

This confusion arises from how _post_init_ is defined.

The Solution: Correctly Naming the _post_init_ Method

The error occurs due to a common typo in the method name. Python dataclasses have a special method named __post_init__, which is meant to run immediately after the class is initialized.

The Incorrect Method Name

In the original code, the developer incorrectly named the method as _post__init_ with two underscores between post and init:

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

The Correct Method Name

To fix the error, the method should be renamed to _post_init_ with only one underscore between post and init:

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

Final Working Code

Here is the corrected version of the code that will run without errors:

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

Conclusion

In summary, the AttributeError experienced due to a misnamed method is a common pitfall when working with Python dataclasses. By simply ensuring that the method is correctly named __post_init__, you can avoid this error and successfully initialize additional attributes after your dataclass creation. Remember, it's the small details that can make a big difference!

By paying close attention to method names and following Python’s conventions, you can streamline your coding process and reduce frustrating errors. Happy coding!