Refactor toward SOLID with pluggable strategies selected by a factory.

Write a parameterized, well-behaved decorator that preserves the wrapped function.

Customize attribute access with a descriptor and understand how classes are created.

Choose a concurrency model and parallelize a batch with a thread pool.

Run many I/O tasks concurrently with coroutines and asyncio.gather.

Find the hot path, fix complexity, and memoize repeated work with lru_cache.

Load typed config from the environment, keep secrets safe, and log structured records.

Design code for testability, mock its dependencies, and know the modern tool stack.

Build a typed, tested, packaged order service that integrates the whole track.