Focused notes from real bug fixes across the Python open-source ecosystem.

This repository collects small, concrete debugging write-ups: what broke, how the failure was reproduced, what made the fix minimal, and what test closed the loop. The goal is to make real maintenance work easier to study than a long commit history or a closed pull request tab.

• Short postmortems for parser, scientific Python, data tooling, serialization, and packaging bugs.
• A checklist for turning a failing behavior into a focused pull request.
• Links to upstream issues and PRs where possible.

1. Reproduce the failure with the smallest input that still fails.
2. Identify the contract being violated.
3. Add or update one targeted regression test.
4. Make the smallest code change that satisfies the contract.
5. Run the narrow test first, then the relevant package test slice.
6. Keep the pull request body factual: bug, cause, fix, verification.

• feedparser: Anchoring Author Email Parsing
• mistune: Preserving RST List Item State
• pyserde: Union Argument Order and Optional Cache Reuse
• mwparserfromhell: Empty-Title Wikilink Filtering
• py7zr: Requiring Passwords for Explicit Crypto Filters
• PyMeasure: Explicit SRS Auxiliary Output Formatting
• sqlparse: Keeping Oracle Procedure Declarations Together
• trimesh: OBJ/MTL Optional Property Round-Trips

## Summary
- Explain the user-visible bug.
- Explain the minimal fix.

## Test
- List the exact command used.

Many useful open-source contributions are small: a one-line formatting fix, a missing edge-case test, or a parser branch that should have accepted valid input. Those fixes are easy to overlook, but they are also the best way to learn maintainable debugging.

This repo is a public index of that work.