Worked on core Python infrastructure, focusing on correctness and type safety across two major repositories. In picnixz/cpython, addressed a subtle data structure issue by aligning UserDict.popitem with standard dict LIFO semantics, updating both implementation and tests to ensure consistent behavior for downstream users. In python/typeshed, introduced generic support for Interpolation in the templatelib module, enabling type parameterization and improving type safety for template strings. Also performed typing compatibility cleanups and enhanced code readability by removing outdated recommendations and unnecessary markers. Leveraged Python, object-oriented programming, and type hinting to deliver maintainable, reliable improvements to foundational Python libraries.