Working on projects

uv supports managing Python projects, which define their dependencies in a pyproject.toml file.

Creating a new project

You can create a new Python project using the uv init command:

$ uv init hello-world
$ cd hello-world

Alternatively, you can initialize a project in the working directory:

$ mkdir hello-world
$ cd hello-world
$ uv init

uv will create the following files:

.
├── .python-version
├── README.md
├── hello.py
└── pyproject.toml

The hello.py file contains a simple "Hello world" program. Try it out with uv run:

$ uv run hello.py
Hello from hello-world!

A project consists of a few important parts that work together and allow uv to manage your project. In addition to the files created by uv init, uv will create a virtual environment and uv.lock file in the root of your project the first time you run a project command, i.e., uv run, uv sync, or uv lock.

A complete listing would look like:

.
├── .venv
│   ├── bin
│   ├── lib
│   └── pyvenv.cfg
├── .python-version
├── README.md
├── hello.py
├── pyproject.toml
└── uv.lock

`pyproject.toml`

The pyproject.toml contains metadata about your project:

pyproject.toml

[project]
name = "hello-world"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
dependencies = []

You'll use this file to specify dependencies, as well as details about the project such as its description or license. You can edit this file manually, or use commands like uv add and uv remove to manage your project from the terminal.

Tip

See the official pyproject.toml guide for more details on getting started with the pyproject.toml format.

You'll also use this file to specify uv configuration options in a [tool.uv] section.

`.python-version`

The .python-version file contains the project's default Python version. This file tells uv which Python version to use when creating the project's virtual environment.

`.venv`

The .venv folder contains your project's virtual environment, a Python environment that is isolated from the rest of your system. This is where uv will install your project's dependencies.

See the project environment documentation for more details.

`uv.lock`

uv.lock is a cross-platform lockfile that contains exact information about your project's dependencies. Unlike the pyproject.toml which is used to specify the broad requirements of your project, the lockfile contains the exact resolved versions that are installed in the project environment. This file should be checked into version control, allowing for consistent and reproducible installations across machines.

uv.lock is a human-readable TOML file but is managed by uv and should not be edited manually.

See the lockfile documentation for more details.

Managing dependencies

You can add dependencies to your pyproject.toml with the uv add command. This will also update the lockfile and project environment:

$ uv add requests

You can also specify version constraints or alternative sources:

$ # Specify a version constraint
$ uv add 'requests==2.31.0'

$ # Add a git dependency
$ uv add git+https://github.com/psf/requests

To remove a package, you can use uv remove:

$ uv remove requests

To upgrade a package, run uv lock with the --upgrade-package flag:

$ uv lock --upgrade-package requests

The --upgrade-package flag will attempt to update the specified package to the latest compatible version, while keeping the rest of the lockfile intact.

See the documentation on managing dependencies for more details.

Running commands

uv run can be used to run arbitrary scripts or commands in your project environment.

Prior to every uv run invocation, uv will verify that the lockfile is up-to-date with the pyproject.toml, and that the environment is up-to-date with the lockfile, keeping your project in-sync without the need for manual intervention. uv run guarantees that your command is run in a consistent, locked environment.

For example, to use flask:

$ uv add flask
$ uv run -- flask run -p 3000

Or, to run a script:

example.py

# Require a project dependency
import flask

print("hello world")

$ uv run example.py

Alternatively, you can use uv sync to manually update the environment then activate it before executing a command:

$ uv sync
$ source .venv/bin/activate
$ flask run -p 3000
$ python example.py

Note

The virtual environment must be active to run scripts and commands in the project without uv run. Virtual environment activation differs per shell and platform.

See the documentation on running commands and running scripts in projects for more details.

Building distributions

uv build can be used to build source distributions and binary distributions (wheel) for your project.

By default, uv build will build the project in the current directory, and place the built artifacts in a dist/ subdirectory:

$ uv build
$ ls dist/
hello-world-0.1.0-py3-none-any.whl
hello-world-0.1.0.tar.gz

See the documentation on building projects for more details.

Next steps

To learn more about working on projects with uv, see the Projects concept page and the command reference.

Or, read on to learn how to publish your project as a package.