feat(prepro): add function to process phenotype_values and extract regex

[anna-parker]

resolves #5902, #5901

Screenshot

This PR is currently being used on the private virus preview:

• https://github.com/loculus-project/private_deployments/blob/main/deploy/virus4/values.yaml#L629
• https://github.com/loculus-project/private_deployments/blob/main/deploy/virus4/values.yaml#L592

PR Checklist

• All necessary documentation has been adapted.
• The implemented feature is covered by appropriate, automated tests.
• Any manual testing that has been done is documented (i.e. what exactly was tested?)

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[claude]

Claude finished @anna-parker's task in 1m 39s —— View job

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Code Review Complete

I've reviewed the PR that adds functionality to process phenotype_values and extract regex patterns. Here's my assessment:

Summary

The implementation adds two useful preprocessing functions (extract_regex and implicit support for phenotype_values processing) that extend the metadata processing capabilities. The code is generally well-structured and follows existing patterns. However, there are several areas that need attention before merging.

Key Issues

Critical:

1. Missing input validation in process_phenotype_values (preprocessing/nextclade/src/loculus_preprocessing/processing_functions.py:1243) - The function doesn't validate that args contains the required "name" key, which could cause KeyError exceptions.

2. Overly broad exception handling (line 1249) - Using bare except Exception could mask programming errors. Should be more specific about expected exceptions from ast.literal_eval.

Important:
3. Incomplete documentation - The process_phenotype_values function is used in the code but not documented in the README alongside the other preprocessing functions.

4. Limited test coverage - The tests for process_phenotype_values (test_nextclade_preprocessing.py:1250) only cover the happy path. Missing tests for error cases, edge cases, and invalid inputs.

5. Ambiguous behavior with duplicates (line 1246) - If multiple phenotype entries have the same name, the function silently returns the last match without warning.

Minor:
6. Type handling - The function converts all values to strings, which might lose type information (e.g., distinguishing between 0.0 and 0).

7. Error messages could be more informative by including which phenotype name was being searched for.

Positive Aspects

• Clean separation of concerns with the process_phenotype_values function
• Good test coverage for the extract_regex functionality with both success and failure cases
• Consistent code style matching the existing codebase
• The regex extraction implementation is robust with proper error handling

Recommendations

1. Add input validation to process_phenotype_values
2. Make exception handling more specific
3. Add comprehensive tests for edge cases and error conditions
4. Document the process_phenotype_values function in the README
5. Consider whether duplicate phenotype names should trigger a warning

The functionality is sound and the implementation follows good patterns, but the missing validation and documentation need to be addressed.

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[anna-parker]

Comment from @rneher in the private preview we use the extract_regex function for obtaining the subtype from the reference name and there it would be good to have the subtype capitalized.

I proposed adding this as an option to the function.