Rust crates for Conda environments

rattler & py-rattler

The rattler crates can be used to build custom applications leveraging Conda packages. Download repodata, solve for package specs and install packages in a few lines of code. The powerful Python bindings allow for even more flexible use cases.

Rust docs

Python docs

A little Rust is all you need

Solve, create and install environments

The rattler crate gives you access to high-level functionality to download channel index data, solve for `MatchSpec`s, and install packages. On top of rattler you can build bespoke tooling to set up custom environments with maximum parallelism and speed – rattler will handle the low-level details.

It's our core building block for Pixi, rattler-build and the backend of the prefix.dev Website.

main.rs

pub async fn create(opt: Opt) -> anyhow::Result<()> {
    let channel_config = ChannelConfig::default_with_root_dir(env::current_dir()?);
    let current_dir = env::current_dir()?;
    let target_prefix = opt
        .target_prefix
        .unwrap_or_else(|| current_dir.join(".prefix"));

    // Make the target prefix absolute
    let target_prefix = std::path::absolute(target_prefix)?;
    println!("Target prefix: {}", target_prefix.display());

    // Determine the platform we're going to install for
    let install_platform = if let Some(platform) = opt.platform {
        Platform::from_str(&platform)?
    } else {
        Platform::current()
    };

    println!("Installing for platform: {install_platform:?}");

    // Parse the specs from the command line. We do this explicitly instead of allow
    // clap to deal with this because we need to parse the `channel_config` when
    // parsing matchspecs.
    let specs = opt
        .specs
        .iter()
        .map(|spec| MatchSpec::from_str(spec, ParseStrictness::Strict))
        .collect::<Result<Vec<_>, _>>()?;

Python bindings

Powerful Python bindings

We expose the power of rattler with Python bindings to make rapid iteration for custom development possible. The bindings give you all the power of rattler in a very convenient form. We think py-rattler is the best way to interact with Conda environments programatically.

Install them with:

pixi add py-rattler

or even from PyPI:

uv / pip add py-rattler

solver.py

import asyncio
import tempfile

from rattler import solve, install, VirtualPackage


async def main() -> None:
    # Start by solving the environment.
    #
    # Solving is the process of going from specifications of package and their
    # version requirements to a list of concrete packages.
    print("started solving the environment")
    solved_records = await solve(
        # Channels to use for solving
        channels=["conda-forge"],
        # The specs to solve for
        specs=["python ~=3.12.0", "pip", "requests 2.31.0"],
        # Virtual packages define the specifications of the environment
        virtual_packages=VirtualPackage.detect(),
    )
    print("solved required dependencies")

    # Install the packages into a new environment (or updates it if it already
    # existed).
    env_path = tempfile.mkdtemp()
    await install(
        records=solved_records,
        target_prefix=env_path,
    )

    print(f"created environment: {env_path}")


if __name__ == "__main__":
    asyncio.run(main())