Implements a `method_cache` decorator that caches method results per instance using a weak-key dictionary. This is a self-contained utility that can be extracted and reused in any Python project to add per-instance caching to methods. It demonstrates careful handling of weak references and dictionary key management.

Provides a keymap compilation system that parses key sequence definitions (e.g., '^A', '\e[1~') and builds a trie-based state machine for efficient dispatch. This is a reusable pattern for any application that needs to map keyboard input to commands, such as terminal editors or custom REPLs. The implementation is clean, well-documented, and independent of the rest of the _pyrepl package.

Defines a generic hash table (`_Py_hashtable_t`) with custom allocators, hash functions, and destroy callbacks. This is a reusable C data structure that can be extracted and used in any C project needing a lightweight, customizable hash table. It demonstrates careful memory management and API design for generic containers.

Provides macros for per-type freelist management (push/pop operations) used to speed up allocation of common objects like tuples and floats. This is a reusable pattern for implementing object pools in C. The macros are self-contained and can be adapted to any type that needs fast allocation/deallocation.

Contains utility functions like `run_concurrently` and `start_threads` that simplify writing multi-threaded tests. These are reusable across any Python project that needs to test concurrent behavior. The implementation handles thread lifecycle, exception propagation, and timeout management cleanly.