I have been using dataclasses in my python data retrieval scripts but on the occasions when a field is added to the API return I needed a way to make the scripts continue to run. The added benefit of notifying the script user about any unknown fields helps too.

The following code with a Warning message to show any fields that are not predefined in the dataclass.

from dataclasses import dataclass
from dataclasses import fields

def filter_unexpected_fields(cls):
    original_init = cls.__init__

    def new_init(self, *args, **kwargs):
        expected_fields = {field.name for field in fields(cls)}
        cleaned_kwargs = {key: value for key, value in kwargs.items() if key in expected_fields}
        unknown_kwargs = {key: value for key, value in kwargs.items() if key not in expected_fields}
        original_init(self, *args, **cleaned_kwargs)
        # Handle unknown fields (optional)
        if unknown_kwargs:
            # Log a warning or raise an exception based on your needs
            print(f"Warning: Unknown fields found: {unknown_kwargs}")
    cls.__init__ = new_init
    return cls

@filter_unexpected_fields
@dataclass
class Application:
     id: int
     name: str

a1 = { 'id': 1, 'name': 'WebGoat',"runs":5}
app = Application(**a1)

So given the following code, the “runs” field is not defined in the dataclass object, but with the “@filter_unexpected_fields” decorator, the code will continue to work but the additional warning message will notify about any undefined fields.
_{¹ based on answer on this page: https://stackoverflow.com/questions/54678337/how-does-one-ignore-extra-arguments-passed-to-a-dataclass}

This entry was posted on Wednesday, July 31st, 2024 at 6:31 am and is filed under Programming, Python. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.