Understanding Type Hints for Custom Class Attributes in Python

Learn how to effectively use `type hints` for custom class attributes in Python, specifically when working across multiple modules.
---
This video is based on the question https://stackoverflow.com/q/67437030/ asked by the user 'Kārlis Rieksts' ( https://stackoverflow.com/u/7844162/ ) and on the answer https://stackoverflow.com/a/67437097/ provided by the user 'chepner' ( https://stackoverflow.com/u/1126841/ ) 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: Type hint for custom class atributes

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

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding Type Hints for Custom Class Attributes in Python

If you're new to Python, you may have encountered the concept of type hints — a way to explicitly specify the expected data types of variables, function arguments, and return types. However, when working with a more complex application that consists of multiple scripts and modules, figuring out how type hints apply can get tricky. This post delves into how to properly utilize type hints in custom classes and across modules, particularly focusing on dictionaries tied to class attributes.

The Problem

You have a main application that creates instances of two classes: FigureFormatter and Plotter. The Plotter class has a method called plot_figure, which takes a parameter styler. This parameter is a dictionary that is defined in FigureFormatter. The challenge arises when trying to effectively hint the type for the styler argument, considering its specific structure and origin.

Here’s a simplified version of the existing code structure:

Main Application

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

FigureFormatter Class

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

Plotter Class

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

The main question to address is: What kind of type hint should be applied to the styler argument in plot_figure, given that it is an attribute of an instance of FigureFormatter?

The Solution: Using TypedDict for Enhanced Type Hints

What is TypedDict?

Introduced in Python 3.8, TypedDict allows you to define a dictionary with specific string keys leading to specific data types. This is very helpful in your case, as it enables you to specify the exact structure of your styler dictionary.

Defining the Typings

In modules/FigureFormatter:

You can create TypedDict definitions for both properties and the overall structure of the dictionary. Below is an example:

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

In modules/Plotter:

You would import Styler and use it in your method definitions like this:

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

Extracting the Dictionary from an Instance

If you want to ensure that the styler dictionary derives from a specific class attribute, an alternative option would be to require an instance of FigureFormatter passed directly into the plot_figure method. You can then extract the styler dictionary directly:

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

Conclusion

Type hints enhance code readability and maintainability, making it clear what you expect as input and output in your functions. By leveraging TypedDict, you can specify the structure of dictionaries, ensuring your code stays organized and understandable, even across multiple modules. Whether you choose to pass just the dictionary or the instance of the class, being explicit about your types will lead to better code practices as your Python applications grow.

Stay tuned for more insights on Python programming techniques and effective practices!

Видео Understanding Type Hints for Custom Class Attributes in Python канала vlogize