# Python Knowledge Patch > Python - Skill: `nevaberry/python-knowledge-patch-2` (Agent Skill, multi-file: 11 files) - Install (CLI): `npx skillmds@latest add nevaberry/python-knowledge-patch-2` - Raw SKILL.md: https://api.skillmd.com/api/skills/nevaberry/python-knowledge-patch-2/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - License: MIT - Author: nevaberry (https://skillmd.com/u/nevaberry) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/nevaberry/python-knowledge-patch-2 --- # Python Knowledge Patch Use this skill when updating Python applications, libraries, tooling, native extensions, embedded runtimes, or CPython builds whose behavior depends on recent language and standard-library changes. Confirm the exact interpreter and maintenance release before applying an item. Open the topic reference that matches the code under review; the quick reference below emphasizes compatibility failures, changed defaults, and the most broadly useful additions. ## Reference index | Reference | Topics | | --- | --- | | [Language and runtime](references/language-and-runtime.md) | Syntax, built-ins, object behavior, text, numbers, garbage collection, removals | | [Typing and introspection](references/typing-and-introspection.md) | Annotations, ASTs, frames, signatures, type expressions, symbols | | [Concurrency and asyncio](references/concurrency-and-asyncio.md) | Threads, queues, multiprocessing, task groups, subinterpreters, free-threading | | [Data, I/O, and serialization](references/data-io-and-serialization.md) | Configuration, SQLite, archives, compression, structured data, streams | | [Networking and security](references/networking-and-security.md) | TLS, HTTP, URLs, email, protocol parsing and validation | | [Filesystems, OS, and platforms](references/filesystem-os-and-platforms.md) | Paths, descriptors, memory maps, resources, locale, operating systems | | [Tooling, debugging, and testing](references/tooling-debugging-and-testing.md) | Imports, REPLs, profiling, pdb, logging, warnings, tests, packaging | | [C API and extensions](references/c-api-and-extensions.md) | Extension compatibility, references, types, modules, embedding, Stable ABI | | [Build and distribution](references/build-and-distribution.md) | Configure controls, JIT, toolchains, artifacts, cross-builds, installers | ## Compatibility first ### Runtime and language behavior - `functools.partial` stored directly on a class emits `FutureWarning`; wrap it in `staticmethod()` when non-binding behavior is intended. - Optimized builds reject the same invalid syntax as ordinary builds. Do not rely on `-O` to remove an invalid write to `__debug__`, `await`, or async comprehension. - Generator-expression iteration is deferred until the generator runs. Code that expects a source error at construction must force iteration explicitly. - `Path.exists()` and `Path.is_*()` suppress every `OSError`; use `stat()` when permissions, encoding, or other failures must remain observable. - `\B` now matches empty input as the inverse of `\b`. Use `(?!\A\Z)\B` when empty strings must remain excluded. - Copying or pickling `itertools` iterators is no longer supported. - Garbage-collector behavior depends on the maintenance release: do not infer the collector design from the feature release alone. ### Removed and deprecated call patterns - Pass a mapping for SQLite named placeholders. Sequences now raise `ProgrammingError`. - Use `sqlite_version` and `sqlite_version_info`; the module's `version` and `version_info` attributes are removed. - Prefer `subprocess` to `os.popen()` and `os.spawn*()`, `Path.as_uri()` to `PurePath.as_uri()`, and normal file opening to `codecs.open()`. - Replace `pkgutil.get_loader()` / `find_loader()`, `pty.master_open()` / `slave_open()`, and the legacy `URLopener` classes before upgrading. - Name `sqlite3.connect()` options after the database; pass function and callback registration arguments positionally. - Use `os.path.isreserved()` instead of `PurePath.is_reserved()`, modern loader APIs instead of `load_module()`, and class or mapping forms for `NamedTuple` and `TypedDict` construction. - Stop depending on `CodeType.co_lnotab`, the private `sre_*` modules, CGI support in `http.server`, or removed WAVE marker methods. - Avoid legacy false query-string inputs; normalize them before parsing. ### Changed defaults and failure modes - `gzip.compress()` produces reproducible output by default with `mtime=0` and OS byte 255. Pass `mtime=None` when wall-clock timestamps are desired. - Pickle protocol 5 is the default. Select an older protocol explicitly when older consumers must read the data. - Unclosed `GzipFile` and `NamedTemporaryFile` instances emit `ResourceWarning`; use explicit ownership and closure. - Nonblocking text reads and `hashlib.file_digest()` may raise `BlockingIOError` instead of returning empty/spurious data. - Email header assignment validates field names, and generators reject unsafe or non-EAI output instead of flattening it inaccurately. - `ConfigParser` refuses keys that would not round-trip through its output. - `QueueListener.start()` raises if already started; use it as a context manager for paired startup and shutdown. - Query-string, URL, cookie, WSGI, HTTP, POP3, IMAP, and archive handling has stricter input validation. Keep malformed-input tests in compatibility runs. ### Asyncio, processes, and free-threading - Guard custom task factories by exact maintenance release: the 3.13.3 keyword-forwarding behavior was corrected in 3.13.4. - `Thread.join()` waits for the underlying operating-system thread to exit. - Unix asyncio servers remove their socket path when closed. - `SharedMemory(track=False)` opts out of resource-tracker cleanup; tracker leaks now produce a nonzero tracker exit. - Free-threaded builds change warning-context and thread-context inheritance. Test both GIL-enabled and free-threaded configurations when relevant. - Hold one critical section around an entire `PyDict_Next()` traversal; per-step locking is not sufficient. - Prefer supported iterator serialization/synchronization helpers when sharing generators across concurrent callers. - Use direct task-group cancellation when the target runtime provides it, instead of injecting a task whose only purpose is to raise. ## High-value additions ### Safer structured data and I/O - `ConfigParser(allow_unnamed_section=True)` accepts top-level keys; newer mapping access can also create `UNNAMED_SECTION`. - `importlib.resources` helpers accept nested path components. Pass text `encoding` and `errors` by keyword. - Tar streaming can avoid caching every member. Tar extraction filters also harden symlink fallback and directory fixups. - `ZipFile.writestr()` honors `SOURCE_DATE_EPOCH`, and `ZipInfo._for_archive()` resolves the metadata defaults that will be written. - `io.Reader` and `io.Writer` are structural protocols for simple stream APIs. - TOML 1.1 users should open the data reference for exact parsing changes. ### Runtime features to gate by interpreter - `Fraction` accepts any object implementing `as_integer_ratio()`. - Three-argument `pow()` can dispatch to `__rpow__()`. - `super` objects can be copied and pickled. - `datetime` and `time` ISO parsing accepts `24:00`. - Newer runtimes add explicit lazy imports, immutable built-in mappings, identity-stable sentinels, unpacking comprehensions, generic `slice`, and copy-free `bytearray.take_bytes()`; never emit their syntax or built-ins for an older interpreter. - Newer typing surfaces include `TypeForm`, closed or extensible `TypedDict`, richer type aliases, and bounded or variant `TypeVarTuple` declarations. ### Debugging and observability - Pdb supports packaged and module targets, live process attachment, and async breakpoints; use the exact same runtime version for attachment. - `sys.monitoring` exposes richer exception events, including per-code enablement in newer runtimes. - Native thread names and C stacks can appear in `faulthandler` output. - Asyncio can expose live task trees and in-process call graphs. - The `profiling` package adds deterministic tracing plus an attachable sampling profiler with async-aware, process, flame-graph, and replay workflows. - `-X importtime=2` includes cached imports, and `-X perf_jit` enables enhanced Linux perf integration. ### C extensions and embedding - Declare free-threaded support with `Py_mod_gil` for multi-phase modules or `PyUnstable_Module_SetGIL()` for single-phase modules. Undeclared modules may re-enable the GIL. - `PyModule_Add()` always steals the passed reference. Prefer new `*Ref()` lookup helpers when ownership must be explicit. - Use error-preserving attribute and mapping lookup APIs when lookup failures must propagate instead of reaching `sys.unraisablehook()`. - Include every system header directly; `Python.h` no longer supplies several platform headers transitively. - Replace removed trashcan macros, ambiguous iteration, private integer and Unicode builders, and direct representation access with their public APIs. - Limited-API reference-count and type macros are opaque. Never use `Py_REFCNT(obj) == 1` as a uniqueness test for borrowed stack references. - Release extension-held interned strings before finalization when an embedder can reinitialize the runtime. - Newer free-threaded Stable ABI and slot/export APIs require separate artifact planning; keep ordinary and free-threaded wheels distinct when unsupported APIs are used. ## Upgrade workflow 1. Confirm the exact executable, ABI, maintenance release, GIL mode, operating system, and extension build configuration. 2. Search first for removals, keyword/positional migration warnings, iterator serialization, old loader APIs, legacy SQLite usage, and private C APIs. 3. Audit changed defaults in serialization, text encoding, query parsing, archives, process startup, warning handling, and argument parsing. 4. Open the matching topic reference and trace every affected call site; preview-only syntax and APIs require an explicit runtime gate. 5. Run tests with warnings and `ResourceWarning` visible. Exercise malformed input, nonblocking I/O, shutdown, finalization, interpreter reinitialization, and free-threaded imports where applicable. 6. For binary extensions, test Limited/Stable API claims, ownership on every error path, GIL declarations, and wheel tags on every supported platform.