Simon Willison’s Weblog

9 items tagged “mypy”


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. # 31st May 2022, 11:24 pm

typesplainer (via) A Python module that produces human-readable English descriptions of Python type definitions—also available as a web interface. # 15th March 2022, 6:18 am

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. # 30th January 2022, 1:31 am


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. # 17th December 2021, 7:43 pm

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. # 18th October 2021, 7:03 pm

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.

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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. # 2nd August 2018, 9:03 pm

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. # 11th May 2018, 5:47 pm

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. # 19th April 2018, 6:30 pm