Puffin

An extremely fast Python package installer and resolver, written in Rust. Designed as a drop-in replacement for pip and pip-compile.

Puffin is backed by Astral, the creators of Ruff.

Highlights

• ⚡️ 10-100x faster than pip and pip-tools (pip-compile and pip-sync).
• 💾 Disk-space efficient, with a global cache for dependency duplication and Copy-on-Write installation on supported platforms.
• 🐍 Installable via pip, pipx, brew etc. Puffin is a single static binary that can be installed without Rust or even a Python environment.
• 🧪 Tested at-scale against the top 10,000 PyPI packages.
• ⚖️ Drop-in replacement for common pip, pip-tools, and virtualenv commands.
• 🤝 Support for a wide range of advanced pip features, including: editable installs, Git dependencies, direct URL dependencies, local dependencies, constraints, source distributions, HTML and JSON indexes, and more.
• 🧰 Novel resolution features such as override of transitive dependency versions and a lowest compatible version resolution strategy.

Getting Started

Puffin is available as puffin on PyPI:

pipx install puffin

To create a virtual environment with Puffin:

puffin venv  # Create a virtual environment at .venv.

To install a package into the virtual environment:

puffin pip install flask                # Install Flask.
puffin pip install -r requirements.txt  # Install from a requirements.txt file.
puffin pip install -e .                 # Install the current project in editable mode.

To generate a set of locked dependencies from an input file:

puffin pip compile pyproject.toml -o requirements.txt   # Read a pyproject.toml file.
puffin pip compile requirements.in -o requirements.txt  # Read a requirements.in file.

To install a set of locked dependencies into the virtual environment:

puffin pip sync requirements.txt  # Install from a requirements.txt file.

Puffin's pip-install and pip-compile commands supports many of the same command-line arguments as existing tools, including -r requirements.txt, -c constraints.txt, -e . (for editable installs), --index-url, and more.

Roadmap

Puffin is an extremely fast Python package resolver and installer, designed as a drop-in replacement for pip and pip-tools (pip-compile and pip-sync).

Puffin is not a complete package manager. Instead, it represents an intermediary goal in our pursuit of a "Cargo for Python": a Python package and project manager that is extremely fast, reliable, and easy to use — a single tool capable of unifying not only pip and pip-tools, but also pipx, virtualenv, tox, setuptools, poetry, pyenv, rye, and more.

In the future, Puffin will be used as the foundation for such a tool: a single binary that bootstraps your Python installation and gives you everything you need to be productive with Python.

In the meantime, though, Puffin's narrower scope allows us to solve many of the low-level problems that are required to build such a package manager (like package installation) while shipping an immediately useful tool with a minimal barrier to adoption. Try it today in lieu of pip and pip-compile.

Limitations

Puffin does not yet support Windows (#73).

Puffin does not support the entire pip feature set. Namely, Puffin won't support the following pip features:

• .egg dependencies
• Editable installs for Git and direct URL dependencies (though editable installs are supported for local dependencies)
• ...

On the other hand, Puffin plans to (but does not currently) support:

• Hash checking
• ...

Like pip-compile, Puffin generates a platform-specific requirements.txt file (unlike, e.g., poetry and pdm, which generate platform-agnostic poetry.lock and pdm.lock files). As such, Puffin's requirements.txt files may not be portable across platforms and Python versions.

Advanced Usage

Python discovery

Puffin itself does not depend on Python, but it does need to locate a Python environment to (1) install dependencies into the environment, and (2) build source distributions.

When running pip sync or pip install, Puffin will search for a virtual environment in the following order:

• An activated virtual environment based on the VIRTUAL_ENV environment variable.
• An activated Conda environment based on the CONDA_PREFIX environment variable.
• A virtual environment at .venv in the current directory, or in the nearest parent directory.

If no virtual environment is found, Puffin will prompt the user to create one in the current directory via puffin venv.

When running pip compile, Puffin does not require a virtual environment and will search for a Python interpreter in the following order:

• An activated virtual environment based on the VIRTUAL_ENV environment variable.
• An activated Conda environment based on the CONDA_PREFIX environment variable.
• A virtual environment at .venv in the current directory, or in the nearest parent directory.
• The Python interpreter available as python3 on the system path (preferring, e.g., python3.7 if --python-version=3.7 is specified).

Dependency caching

Puffin uses aggressive caching to avoid re-downloading (and re-building dependencies) that have already been accessed in prior runs.

The specifics of Puffin's caching semantics vary based on the nature of the dependency:

• For registry dependencies (like those downloaded from PyPI), Puffin respects HTTP caching headers.
• For direct URL dependencies, Puffin respects HTTP caching headers, and also caches based on the URL itself.
• For Git dependencies, Puffin caches based on the fully-resolved Git commit hash. As such, puffin pip compile will pin Git dependencies to a specific commit hash when writing the resolved dependency set.
• For local dependencies, Puffin caches based on the last-modified time of the setup.py or pyproject.toml file.

If you're running into caching issues, Puffin includes a few escape hatches:

• To force Puffin to ignore cached data for all dependencies, run puffin pip install --reinstall ....
• To force Puffin to ignore cached data for a specific dependency, run, e.g., puffin pip install --reinstall-package flask ....
• To clear the global cache entirely, run puffin clean.

Resolution strategy

By default, Puffin follows the standard Python dependency resolution strategy of preferring the latest compatible version of each package. For example, puffin pip install flask>=2.0.0 will install the latest version of Flask (at time of writing: 3.0.0).

However, Puffin's resolution strategy be configured to prefer the lowest compatible version of each package (--resolution=lowest), or even the lowest compatible version of any direct dependencies (--resolution=lowest-direct), both of which can be useful for library authors looking to test their packages against the oldest supported versions of their dependencies.

For example, given the following requirements.in file:

flask>=2.0.0

Running puffin pip compile requirements.in would produce the following requirements.txt file:

# This file was autogenerated by Puffin v0.0.1 via the following command:
#    puffin pip compile requirements.in
blinker==1.7.0
    # via flask
click==8.1.7
    # via flask
flask==3.0.0
itsdangerous==2.1.2
    # via flask
jinja2==3.1.2
    # via flask
markupsafe==2.1.3
    # via
    #   jinja2
    #   werkzeug
werkzeug==3.0.1
    # via flask

However, puffin pip compile --resolution=lowest requirements.in would instead produce:

# This file was autogenerated by Puffin v0.0.1 via the following command:
#    puffin pip compile requirements.in --resolution=lowest
click==7.1.2
    # via flask
flask==2.0.0
itsdangerous==2.0.0
    # via flask
jinja2==3.0.0
    # via flask
markupsafe==2.0.0
    # via jinja2
werkzeug==2.0.0
    # via flask

Pre-release handling

By default, Puffin will accept pre-release versions during dependency resolution in two cases:

1. If the package is a direct dependency, and its version markers include a pre-release specifier (e.g., flask>=2.0.0rc1).
2. If all published versions of a package are pre-releases.

If dependency resolution fails due to a transitive pre-release, Puffin will prompt the user to re-run with --prerelease=allow, to allow pre-releases for all dependencies.

Alternatively, you can add the transitive dependency to your requirements.in file with pre-release specifier (e.g., flask>=2.0.0rc1) to opt in to pre-release support for that specific dependency.

Pre-releases are notoriously difficult to model, and are a frequent source of bugs in other packaging tools. Puffin's pre-release handling is intentionally limited and intentionally requires user intervention to opt in to pre-releases to ensure correctness, though pre-release handling will be revisited in future releases.

Dependency overrides

Historically, pip has supported "constraints" (-c constraints.txt), which allows users to narrow the set of acceptable versions for a given package.

Puffin supports constraints, but also takes this concept further by allowing users to override the acceptable versions of a package across the dependency tree via overrides (-o overrides.txt).

In short, overrides allow the user to lie to the resolver by overriding the declared dependencies of a package. Overrides are a useful last resort for cases in which the user knows that a dependency is compatible with a newer version of a package than the package declares, but the package has not yet been updated to declare that compatibility.

For example, if a transitive dependency declares pydantic>=1.0,<2.0, but the user knows that the package is compatible with pydantic>=2.0, the user can override the declared dependency with pydantic>=2.0,<3 to allow the resolver to continue.

While constraints are purely additive, and thus cannot expand the set of acceptable versions for a package, overrides can expand the set of acceptable versions for a package, providing an escape hatch for erroneous upper version bounds.

Multi-version resolution

Puffin's pip-compile command produces a resolution that's known to be compatible with the current platform and Python version. Unlike Poetry, PDM, and other package managers, Puffin does not yet produce a machine-agnostic lockfile.

However, Puffin does support resolving for alternate Python versions via the --python-version command line argument. For example, if you're running Puffin on Python 3.9, but want to resolve for Python 3.8, you can run puffin pip compile --python-version=3.8 requirements.in to produce a Python 3.8-compatible resolution.

Acknowledgements

Puffin's dependency resolver uses PubGrub under the hood. We're grateful to the PubGrub maintainers, especially Jacob Finkelman, for their support.

Puffin's Git implementation draws on details from Cargo.

Some of Puffin's optimizations are inspired by the great work we've seen in Orogene and Bun. We've also learned a lot from Nathaniel J. Smith's Posy and adapted its trampoline.

License

Puffin is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Puffin by you, as defined in the Apache-2.0 license, shall be dually licensed as above, without any additional terms or conditions.