Worked on the Optuna repository over a two-month period, focusing on code quality and maintainability through targeted refactoring and type hinting enhancements. Improved static analysis and developer experience by conditionalizing imports with TYPE_CHECKING, ensuring type hints were available without incurring runtime overhead. Refactored string formatting to use Python f-strings, increasing code readability and aligning with modern best practices. Enhanced test modules by moving imports to TYPE_CHECKING blocks, reducing memory usage and startup time. Emphasized Python and testing skills throughout, delivering features that prepared the codebase for safer future changes while maintaining performance and clarity without introducing customer-facing updates.