Not having ID break index cache key across Python invocations

[jamesbraza]

#1125 differentiated cache keys across PDF parse functions, but inadvertently exposed us to this:

from paperqa_pypdf import parse_pdf_to_pages

print(str(parse_pdf_to_pages))  # '<function parse_pdf_to_pages at 0x1037180e0>'

Namely, the ID shown in the str representation is breaking the cache key across Python invocations 🫠. This PR:

• Uses a more stable FQN for this path
• Also handles lambda and functools.partial

Closes #1257

[dosubot]

Related Documentation

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[Copilot]

Pull request overview

This PR fixes cache key instability caused by function memory addresses appearing in string representations across Python invocations. The fix introduces a new utility function get_stable_str() that generates stable string representations for functions, handling special cases like lambdas and functools.partial objects.

Key changes:

• Added get_stable_str() utility function to generate stable function identifiers using fully qualified names (FQN) for normal functions and code hashes for lambdas/partials
• Updated ParsingSettings._custom_serializer() to use get_stable_str() for JSON-safe serialization
• Modified Settings.get_index_name() to use get_stable_str() for stable cache key generation
• Added test cases for lambda and partial function handling

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/paperqa/utils.py	Added get_stable_str() function to generate stable string representations for functions, avoiding memory address issues in cache keys
src/paperqa/settings.py	Updated serialization and index name generation to use get_stable_str() instead of direct string conversion
tests/test_paperqa.py	Added test stubs and test cases to verify lambda and partial functions don't break serialization

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