Скачать или смотреть Easily Create Instantiable Classes from a Python Protocol Using dataclasses.make_dataclass

Learn how to convert a Python Protocol with attribute-only definitions into an instantiable dataclass without redeclaring attributes by using typing.get_type_hints and dataclasses.make_dataclass.
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This video is based on the question https://stackoverflow.com/q/79505837/ asked by the user 'Jan Šimbera' ( https://stackoverflow.com/u/2420452/ ) and on the answer https://stackoverflow.com/a/79506720/ provided by the user 'Kenny Ostrom' ( https://stackoverflow.com/u/1766544/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Problem: Instantiating a Python Protocol with Attributes

Python's Protocol classes are ideal for defining structural interfaces with attribute type annotations, but they cannot be instantiated directly. This is a common roadblock when you want a simple concrete class matching the protocol for testing or other purposes.

Example of a protocol defining an attribute:

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

Trying to instantiate by making it a dataclass:

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

Output:

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

How can we create a concrete class that matches the protocol without duplicating attribute definitions?



Solution: Use get_type_hints with dataclasses.make_dataclass

The essence is to extract attribute definitions from the protocol’s type annotations, then dynamically create a new dataclass that matches those attributes.

Step-by-step:

Use typing.get_type_hints() to retrieve the annotated attributes from the protocol.

Pass these annotations to dataclasses.make_dataclass() to create a new dataclass dynamically.

This avoids messing with internal attributes, keeps the code clean, and requires no manual redefinition.

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

Why this works

get_type_hints fetches a clean dictionary of attribute names and types.

make_dataclass accepts a dictionary of fields and their types and returns a working dataclass.

The result is a class compatible with the protocol's interface and fully instantiable.



Summary

To instantiate a Python attribute-only Protocol:

Extract attribute hints with get_type_hints().

Use dataclasses.make_dataclass() to create a concrete class dynamically.

This approach is concise, avoids boilerplate, and leverages Python's built-in reflection and dataclass capabilities.