Simon Willison’s Weblog

Ruff v0.4.0: a hand-written recursive descent parser for Python. The latest release of Ruff—a Python linter and formatter, written in Rust—includes a complete rewrite of the core parser. Previously Ruff used a parser borrowed from RustPython, generated using the LALRPOP parser generator. Victor Hugo Gomes contributed a new parser written from scratch, which provided a 2x speedup and also added error recovery, allowing parsing of invalid Python—super-useful for a linter.

I tried Ruff 0.4.0 just now against Datasette—a reasonably large Python project—and it ran in less than 1/10th of a second. This thing is Fast. # 19th April 2024, 5 am

How we built JSR (via) Really interesting deep dive by Luca Casonato into the engineering behind the new JSR alternative JavaScript package registry launched recently by Deno.

The backend uses PostgreSQL and a Rust API server hosted on Google Cloud Run.

The frontend uses Fresh, Deno’s own server-side JavaScript framework which leans heavily in the concept of “islands”—a progressive enhancement technique where pages are rendered on the server and small islands of interactivity are added once the page has loaded. # 12th April 2024, 3:49 pm

uv: Python packaging in Rust (via) “uv is an extremely fast Python package installer and resolver, written in Rust, and designed as a drop-in replacement for pip and pip-tools workflows.”

From Charlie Marsh and Astral, the team behind Ruff, who describe it as a milestone in their pursuit of a “Cargo for Python”.

Also in this announcement: Astral are taking over stewardship of Armin Ronacher’s Rye packaging tool, another Rust project.

uv is reported to be 8-10x faster than regular pip, increasing to 80-115x faster with a warm global module cache thanks to copy-on-write and hard links on supported filesystems—which saves on disk space too.

It also has a --resolution=lowest option for installing the lowest available version of dependencies—extremely useful for testing, I’ve been wanting this for my own projects for a while.

Also included: “uv venv”—a fast tool for creating new virtual environments with no dependency on Python itself. # 15th February 2024, 7:57 pm

Rye: Added support for marking virtualenvs ignored for cloud sync (via) A neat feature in the new Rye 0.22.0 release. It works by using an xattr Rust crate to set the attributes “com.dropbox.ignored” and “com.apple.fileprovider.ignore#P” on the folder. # 10th February 2024, 6:50 am

NYT Flash-based visualizations work again. The New York Times are using the open source Ruffle Flash emulator—built using Rust, compiled to WebAssembly—to get their old archived data visualization interactives working again. # 21st January 2024, 5:58 am

Fastest Way to Read Excel in Python (via) Haki Benita produced a meticulously researched and written exploration of the options for reading a large Excel spreadsheet into Python. He explored Pandas, Tablib, Openpyxl, shelling out to LibreOffice, DuckDB and python-calamine (a Python wrapper of a Rust library). Calamine was the winner, taking 3.58s to read 500,00 rows—compared to Pandas in last place at 32.98s. # 3rd January 2024, 8:04 pm

ast-grep (via) There are a lot of interesting things about this year-old project.

sg (an alias for ast-grep) is a CLI tool for running AST-based searches against code, built in Rust on top of the Tree-sitter parsing library. You can run commands like this:

sg -p ’await await_me_maybe($ARG)’ datasette --lang python

To search the datasette directory for code that matches the search pattern, in a syntax-aware way.

It works across 19 different languages, and can handle search-and-replace too, so it can work as a powerful syntax-aware refactoring tool.

My favourite detail is how it’s packaged. You can install the CLI utility using Homebrew, Cargo, npm or pip/pipx—each of which will give you a CLI tool you can start running. On top of that it provides API bindings for Rust, JavaScript and Python! # 10th December 2023, 7:56 pm

Writing Python like it’s Rust (via) Fascinating article by Jakub Beránek describing in detail patterns for using type annotations in Python inspired by working in Rust. I learned new tricks about both languages from reading this. # 21st May 2023, 12:18 am

Rye. Armin Ronacher’s take on a Python packaging tool. There are a lot of interesting ideas in this one—it’s written in Rust, configured using pyproject.toml and has some very strong opinions, including completely hiding pip from view and insisting you use “rye add package” instead. Notably, it doesn’t use the system Python at all: instead, it downloads a pre-compiled standalone Python from Gregory Szorc’s python-build-standalone project—the same approach I used for the Datasette Desktop Electron app.

Armin warns that this is just an exploration, with no guarantees of future maintenance—and even has an issue open titled “Should Rye exist?” # 24th April 2023, 4:02 am

How Discord Stores Trillions of Messages (via) This is a really interesting case-study. Discord migrated from MongoDB to Cassandra back in 2016 to handle billions of messages. Today they’re handling trillions, and they completed a migration from Cassandra to Scylla, a Cassandra-like data store written in C++ (as opposed to Cassandra’s Java) to help avoid problems like GC pauses. In addition to being a really good scaling war story this has some interesting details about their increased usage of Rust. As a fan of request coalescing (which I’ve previously referred to as dogpile prevention) I particularly liked this bit:

“Our data services sit between the API and our ScyllaDB clusters. They contain roughly one gRPC endpoint per database query and intentionally contain no business logic. The big feature our data services provide is request coalescing. If multiple users are requesting the same row at the same time, we’ll only query the database once. The first user that makes a request causes a worker task to spin up in the service. Subsequent requests will check for the existence of that task and subscribe to it. That worker task will query the database and return the row to all subscribers.” # 8th March 2023, 7:07 pm

The technology behind GitHub’s new code search (via) I’ve been a beta user of the new GitHub code search for a while and I absolutely love it: you really can run a regular expression search across the entire of GitHub, which is absurdly useful for both finding code examples of under-documented APIs and for seeing how people are using open source code that you have released yourself. It turns out GitHub built their own search engine for this from scratch, called Blackbird. It’s implemented in Rust and makes clever use of sharded ngram indexes—not just trigrams, because it turns out those aren’t quite selective enough for a corpus that includes a lot of three letter keywords like “for”.

I also really appreciated the insight into how they handle visibility permissions: they compile those into additional internal search clauses, resulting in things like “RepoIDs(...) or PublicRepo()” # 6th February 2023, 6:38 pm

sqlite-jsonschema. “A SQLite extension for validating JSON objects with JSON Schema”, building on the jsonschema Rust crate. SQLite and JSON are already a great combination—Alex suggests using this extension to implement check constraints to validate JSON columns before inserting into a table, or just to run queries finding existing data that doesn’t match a given schema. # 28th January 2023, 3:50 am

sqlite-ulid. Alex Garcia’s sqlite-ulid adds lightning-fast SQL functions for generating ULIDs—Universally Unique Lexicographically Sortable Identifiers. These work like UUIDs but are smaller and faster to generate, and can be canonically encoded as a URL-safe 26 character string (UUIDs are 36 characters). Again, this builds on a Rust crate—ulid-rs—and can generate 1 million byte-represented ULIDs with the ulid_bytes() function in just 88.4ms. # 28th January 2023, 3:45 am

sqlite-fastrand. Alex Garcia just dropped three new SQLite extensions, and I’m going to link to all of them. The first is sqlite-fastrand, which adds new functions for generating random numbers (and alphanumeric characters too). Impressively, these out-perform the default SQLite random() and randomblob() functions by about 1.6-2.6x, thanks to being built on the Rust fastrand crate which builds on wyhash, an extremely fast (though not cryptographically secure) hashing function. # 28th January 2023, 3:41 am

datasette-granian (via) Granian is a new Python web server—similar to Gunicorn—written in Rust. I built a small plugin that adds a “datasette granian” command starting a Granian server that serves Datasette’s ASGI application, using the same pattern as my existing datasette-gunicorn plugin. # 20th January 2023, 2:12 am

Servo to Advance in 2023 (via) This is excellent news: Serve, the browser-in-Rust project started by Mozilla in 2012 that produced the Rust programming language, is getting re-activated with four new full-time developers provided by Igalia.

Igalia are a fascinating organization—I hadn’t realized quite how influential they’ve been until I read their Wikipedia page just now

They’ve been around since 2001, and “in 2019 they were the #2 committers to both the WebKit and Chromium codebases and in the top 10 contributors to Gecko/Servo”—including implementing and maintaining CSS Grid Layout! # 16th January 2023, 5:08 pm

Introducing sqlite-xsv: The Fastest CSV Parser for SQLite. Alex Garcia continues to push the boundaries of SQLite extensions. This new extension in Rust wraps the lightning fast Rust csv crate and provides a new csv_reader() virtual table that can handle regular, gzipped and zstd compressed files. # 14th January 2023, 9:54 pm

Data-driven performance optimization with Rust and Miri (via) Useful guide to some Rust performance optimization tools. Miri can be used to dump out a detailed JSON profile of a program which can then be opened and explored using the Chrome browser’s performance tool. # 9th December 2022, 5:19 pm

Introducing sqlite-loadable-rs: A framework for building SQLite Extensions in Rust. Alex Garcia has built a new Rust library for creating SQLite extensions—initially supporting custom scalar functions, virtual tables and table functions and with more types of extension coming soon. This looks very easy to use, partly because the documentation and examples are already delightfully thorough, especially for an initial release. # 7th December 2022, 11:08 pm

Building a BFT JSON CRDT (via) Jacky Zhao describes their project to build a CRDT library for JSON data in Rust, and includes a thorough explanation of what CRDTs are and how they work. “I write this blog post mostly as a note to my past self, distilling a lot of what I’ve learned since into a blog post I wish I had read before going in”—the best kind of blog post! # 21st November 2022, 7:56 pm

Blessed.rs Crate List (via) Rust doesn’t have a very large standard library, so part of learning Rust is figuring out which of the third-party crates are the best for tackling common problems. This here is an opinionated guide to crates, which looks like it could be really useful. # 7th November 2022, 7:25 pm

mitsuhiko/insta (via) I asked for recommendations on Twitter for testing libraries in other languages that would give me the same level of delight that I get from pytest. Two people pointed me to insta by Armin Ronacher, a Rust testing framework for “snapshot testing” which automatically records reference values to your repository, so future tests can spot if they change. # 31st October 2022, 1:06 am

py2rs. Extremely useful document providing resources for learning Rust followed by an extensive collection of common Python tasks (building a list, opening a file, spawning a thread, running a simple web server) and their Rust equivalents. # 7th October 2022, 5:44 pm

libsql (via) A brand new Apache 2 licensed fork of SQLite. The README explains the rationale behind the project: SQLite itself is open source but not open contribution, and this fork aims to try out new ideas. The most interesting to me so far is a plan to support user defined functions implemented in WebAssembly. The project also intends to use Rust for new feature development. # 4th October 2022, 4:13 pm

Turning SQLite into a distributed database (via) Heyang Zhou introduces mvSQLite, his brand new open source “SQLite-compatible distributed database” built in Rust on top of Apple’s FoundationDB. This is a very promising looking new entry into the distributed/replicated SQLite space: FoundationDB was designed to provide low-level primitives that tools like this could build on top of. # 21st August 2022, 5:40 pm

sqlite-zstd: Transparent dictionary-based row-level compression for SQLite. Interesting SQLite extension from phiresky, the author of that amazing SQLite WASM hack from a while ago which could fetch subsets of a large SQLite database using the HTTP range header. This extension, written in Rust, implements row-level compression for a SQLite table by creating compression dictionaries for larger chunks of the table, providing better results than just running compression against each row value individually. # 9th August 2022, 9:23 pm

The State of WebAssembly 2022. Colin Eberhardt talks through the results of the State of WebAssembly 2022 survey. Rust continues to dominate as the most popular language for working to WebAssembly, but Python has a notable increase of interest. # 20th June 2022, 6:07 pm

Why Rust’s postfix await syntax is good (via) C J Silverio explains postfix await in Rust—where you can write a line like this, with the ? causing any errors to be caught and turned into an error return from your function:

let count = fetch_all_animals().await?.filter_for_hedgehogs().len(); # 15th May 2022, 2:27 pm

jless (via) A really nice new command-line JSON viewer, written in Rust, created by Paul Julius Martinez. It provides a terminal interface for navigating through large JSON files, including expanding and contracting nested objects and searching for strings or a modified form of regular expressions. # 12th February 2022, 3:17 am