Ruff 0.16.0 enables 413 rules by default, plus Docker and ty tutorials

Ruff 0.16.0 expanded its default ruleset from 59 rules to 413, a 7x jump. If your project uses Ruff and hasn't upgraded, the next ruff check will flag things it was silently skipping.

New on the handbook

• Build a production Docker image for a uv project Four optimizations (multi-stage build, layer caching, .venv copy, bytecode compilation) cut a FastAPI container from 306 MB to 223 MB and make rebuilds finish in seconds. Starts from a working uv project and ends with a production-ready Dockerfile.

• Set up type checking for a Python project with ty Installs ty into a uv project, plants three bugs a test suite would miss, then shows what ty catches and how to tune rule levels in pyproject.toml. Covers installation through suppression comments.

• Fix ModuleNotFoundError: No module named 'package' One diagnostic command identifies which of five causes broke the import: wrong Python, wrong environment, Jupyter kernel mismatch, or VS Code interpreter mismatch. Each cause has a fix.

• Debug uv dependency resolution failures When uv lock prints No solution found, this how-to walks through reading the conflict chain, inverting the dependency tree to find the responsible package, and applying overrides or constraints to unblock resolution.

From the blog

• Ruff 0.16.0 Enables 7x More Rules by Default A breakdown of every new category now on by default, including bugbear, pyupgrade, simplify, pylint, and more, with a pyproject.toml snippet to freeze the old selection for incremental upgrades.

• uv's Malware Check: What It Blocks and What It Misses uv added install-time malware scanning. The post covers what signals it checks for, what it cannot detect, and why it doesn't replace a lockfile.

In the ecosystem

• uv 0.12.0 changed uv init to create packaged projects by default, with a src/ layout and uv_build. The previous flat layout is now uv init --no-package. If you script project creation, update your commands. Release notes

• Python 3.15.0rc1 shipped August 4; final release targets October. Headline features: lazy import syntax from PEP 810 (up to 70% startup speedup on large codebases), a built-in frozendict type, and the Tachyon statistical profiler. What's new in 3.15

• mypy 2.3 dropped Python 3.9 support for running mypy itself and now respects __new__() return-type annotations that earlier versions ignored. Code targeting 3.9 still works with --python-version 3.9. Changelog

One thing worth trying

Load a .env file without installing python-dotenv:

uv run --env-file .env python script.py

uv run injects variables from .env before Python starts, so os.environ sees them immediately. Pass the flag multiple times to layer files; later files override earlier ones. Set UV_ENV_FILE=.env in your shell to skip the flag on every run.

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