10 posts tagged “mypy”
2025
astral-sh/ty (via) Astral have been working on this "extremely fast Python type checker and language server, written in Rust" quietly but in-the-open for a while now. Here's the first alpha public release - albeit not yet announced - as ty on PyPI (nice donated two-letter name!)
You can try it out via uvx like this - run the command in a folder full of Python code and see what comes back:
uvx ty check
I got zero errors for my recent, simple condense-json library and a ton of errors for my more mature sqlite-utils library - output here.
It really is fast:
cd /tmp
git clone https://github.com/simonw/sqlite-utils
cd sqlite-utils
time uvx ty check
Reports it running in around a tenth of a second (0.109 total wall time) using multiple CPU cores:
uvx ty check 0.18s user 0.07s system 228% cpu 0.109 total
Running time uvx mypy . in the same folder (both after first ensuring the underlying tools had been cached) took around 7x longer:
uvx mypy . 0.46s user 0.09s system 74% cpu 0.740 total
This isn't a fair comparison yet as ty still isn't feature complete in comparison to mypy.
2022
Compiling Black with mypyc (via) Richard Si is a Black contributor who recently obtained a 2x performance boost by compiling Black using the mypyc tool from the mypy project, which uses Python type annotations to generate a compiled C version of the Python logic. He wrote up this fantastic three-part series describing in detail how he achieved this, including plenty of tips on Python profiling and clever optimization tricks.
typesplainer (via) A Python module that produces human-readable English descriptions of Python type definitions—also available as a web interface.
Mypyc (via) Spotted this in the Black release notes: “Black is now compiled with mypyc for an overall 2x speed-up”. Mypyc is a tool that compiles Python modules (written in a subset of Python) to C extensions—similar to Cython but using just Python syntax, taking advantage of type annotations to perform type checking and type inference. It’s part of the mypy type checking project, which has been using it since 2019 to gain a 4x performance improvement over regular Python.
2021
TypeScript for Pythonistas (via) Really useful explanation of how TypeScript differs from Python with mypy. I hadn’t realized TypeScript leans so far into structural typing, to the point that two types with different names but the same “shape” are identified as being the same type as each other.
Tests aren’t enough: Case study after adding type hints to urllib3. Very thorough write-up by Seth Michael Larson describing what it took for the urllib3 Python library to fully embrace mypy and optional typing and what they learned along the way.
Datasette on Codespaces, sqlite-utils API reference documentation and other weeknotes
This week I broke my streak of not sending out the Datasette newsletter, figured out how to use Sphinx for Python class documentation, worked out how to run Datasette on GitHub Codespaces, implemented Datasette column metadata and got tantalizingly close to a solution for an elusive Datasette feature.
[... 2,164 words]2018
Datasette unit tests: monkeytype_call_traces (via) Faceted browse against every function call that occurs during the execution of Datasette’s test suite. I used Instagram’s MonkeyType tool to generate this, which can run Python code and generates a SQLite database of all of the traced calls. It’s intended to be used to automatically add mypy annotations to your code, but since it produces a SQLite database as a by-product I’ve started exploring the intermediary format using Datasette. Generating this was as easy as running “monkeytype run `which pytest`” in the Datasette root directory.
Pyre: Fast Type Checking for Python (via) Facebook’s alternative to mypy. “Pyre is designed to be highly parallel, optimizing for near-instant responses so that you get immediate feedback, even in a large codebase”. Like their Hack type checker for PHP, Pyre is implemented in OCaml.
How to Use Static Type Checking in Python 3.6 (via) Useful introduction to optional static typing in Python 3.6, including how to use mypy, PyCharm and the Atom mypy plugin.