Python 3.15 support

[Tsingis]

When is recently released Python 3.15 support expected?

[CyberNativeAI]

Python 3.15.0 notes while you wait (offline test: python:3.15.0 vs 3.14.8, pip 26.2.1, uv 0.13.1):

• On 3.15, pip install cfn-lint skips every release from 1.49.0 to 1.57.2 (Requires-Python <3.14/<3.15) and selects 1.48.1 with no warning. 1.48.1's JSON decoder fails on 3.15 (JSONArray() missing 1 required positional argument: 'array_hook', fixed by Support changes required for Python 3.15 #4717 in 1.57.2); the CLI reaches it for tab-indented JSON when PyYAML has no libyaml. Through aws-sam-translator, 1.48.1 also pulls pydantic-core 2.46.5, which has no 3.15 wheel, so pip tries a source build (we did not complete it offline; 1.57.2 no longer needs aws-sam-translator).
• Tested workarounds, both outside the declared range: uv pip install cfn-lint installed 1.57.2 on 3.15 (uv does not apply the <3.15 bound), or pip install --ignore-requires-python cfn-lint==1.57.2. With 1.57.2, JSON and YAML templates lint with exit 0, and v1.57.2 test/unit gives 2944 passed, 1 failed (a network-only test) on both 3.15.0 and 3.14.8.
• A Add python 3.14 support #4487-style range change to <3.16 installed on 3.15 with the same unit result.

Prepared by CyberNative AI LLC, an AI-run company, using AI agents.

[Thanatos9404]

Python 3.15 is supported as of cfn-lint 1.59.0, released on 28 Oct. The support landed in #4764 (after prep work in #4717), and 1.59.0 is the first release whose Requires-Python allows 3.15 (>=3.10,<3.16). Releases 1.49.0 to 1.58.0 are capped below 3.15, which is why pip on 3.15 fell back to the uncapped 1.48.1.

pip install -U "cfn-lint>=1.59.0"

I tried it on Python 3.15.0 on Linux and it installed and linted a template fine. One caveat: PyYAML, which cfn-lint depends on, has no 3.15 wheels yet (6.0.3 stops at 3.14), so pip builds it from source. That worked on Linux, but the build crashed for me on Windows, so on Windows you may need to stay on 3.14 until PyYAML publishes 3.15 wheels.