Abstract
This disclosure proposes a gated upgrade model for the Python programming language that allows developers to adopt new runtime semantics, safer defaults, and modern concurrency primitives without breaking existing code. The design introduces an opt-in feature gate (from __future__ import python4_strict) on Python 3.x that enables UTC-aware datetimes, strict UTF-8 I/O, structured concurrency, and type-safe defaults at the module level. In Python 4.0, these semantics become the default, with a one-release rollback option for compatibility.
The proposal also includes tools for migration (refactor4 codemod framework), standardized packaging (pyproject.lock.json), and concurrency enhancements (TaskGroups, cancellation scopes, optional GIL-free mode). A governance model with sub-PEPs (4a–4f) and a phased rollout plan ensures ecosystem stability. This approach enables Python to evolve safely and predictably, addressing long-standing issues from the 2→3 transition while preparing the ecosystem for high-concurrency and AI-driven workloads.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Walker, Joseph JM, "Python 4.0 — A Gated, Forward-Safe Evolution", Technical Disclosure Commons, (October 23, 2025)
https://www.tdcommons.org/dpubs_series/8766