Running scripts

A Python script is a file intended for standalone execution, e.g., with python <script>.py. Using uv to execute scripts ensures that script dependencies are managed without manually managing environments.

Note

If you are not familiar with Python environments: every Python installation has an environment that packages can be installed in. Typically, creating virtual environments is recommended to isolate packages required by each script. uv automatically manages virtual environments for you and prefers a declarative approach to dependencies.

Running a script without dependencies

If your script has no dependencies, you can execute it with uv run:

example.py

print("Hello world")

$ uv run example.py
Hello world

Similarly, if your script depends on a module in the standard library, there's nothing more to do:

example.py

import os

print(os.path.expanduser("~"))

$ uv run example.py
/Users/astral

Arguments may be provided to the script:

example.py

import sys

print(" ".join(sys.argv[1:]))

$ uv run example.py test
test

$ uv run example.py hello world!
hello world!

Additionally, your script can be read directly from stdin:

$ echo 'print("hello world!")' | uv run -

Or, if your shell supports here-documents:

uv run - <<EOF
print("hello world!")
EOF

Note that if you use uv run in a project, i.e. a directory with a pyproject.toml, it will install the current project before running the script. If your script does not depend on the project, use the --no-project flag to skip this:

$ # Note, it is important that the flag comes _before_ the script
$ uv run --no-project example.py

See the projects guide for more details on working in projects.

Running a script with dependencies

When your script requires other packages, they must be installed into the environment that the script runs in. uv prefers to create these environments on-demand instead of using a long-lived virtual environment with manually managed dependencies. This requires explicit declaration of dependencies that are required for the script. Generally, it's recommended to use a project or inline metadata to declare dependencies, but uv supports requesting dependencies per invocation as well.

For example, the following script requires rich.

example.py

import time
from rich.progress import track

for i in track(range(20), description="For example:"):
    time.sleep(0.05)

If executed without specifying a dependency, this script will fail:

$ uv run --no-project example.py
Traceback (most recent call last):
  File "/Users/astral/example.py", line 2, in <module>
    from rich.progress import track
ModuleNotFoundError: No module named 'rich'

Request the dependency using the --with option:

$ uv run --with rich example.py
For example: ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:01

Constraints can be added to the requested dependency if specific versions are needed:

$ uv run --with 'rich>12,<13' example.py

Multiple dependencies can be requested by repeating with --with option.

Note that if uv run is used in a project, these dependencies will be included in addition to the project's dependencies. To opt-out of this behavior, use the --no-project flag.

Creating a Python script

Python recently added a standard format for inline script metadata. It allows for selecting Python versions and defining dependencies. Use uv init --script to initialize scripts with the inline metadata:

$ uv init --script example.py --python 3.12

Declaring script dependencies

The inline metadata format allows the dependencies for a script to be declared in the script itself.

uv supports adding and updating inline script metadata for you. Use uv add --script to declare the dependencies for the script:

$ uv add --script example.py 'requests<3' 'rich'

This will add a script section at the top of the script declaring the dependencies using TOML:

example.py

# /// script
# dependencies = [
#   "requests<3",
#   "rich",
# ]
# ///

import requests
from rich.pretty import pprint

resp = requests.get("https://peps.python.org/api/peps.json")
data = resp.json()
pprint([(k, v["title"]) for k, v in data.items()][:10])

uv will automatically create an environment with the dependencies necessary to run the script, e.g.:

$ uv run example.py
[
│   ('1', 'PEP Purpose and Guidelines'),
│   ('2', 'Procedure for Adding New Modules'),
│   ('3', 'Guidelines for Handling Bug Reports'),
│   ('4', 'Deprecation of Standard Modules'),
│   ('5', 'Guidelines for Language Evolution'),
│   ('6', 'Bug Fix Releases'),
│   ('7', 'Style Guide for C Code'),
│   ('8', 'Style Guide for Python Code'),
│   ('9', 'Sample Plaintext PEP Template'),
│   ('10', 'Voting Guidelines')
]

Important

When using inline script metadata, even if uv run is used in a project, the project's dependencies will be ignored. The --no-project flag is not required.

uv also respects Python version requirements:

example.py

# /// script
# requires-python = ">=3.12"
# dependencies = []
# ///

# Use some syntax added in Python 3.12
type Point = tuple[float, float]
print(Point)

Note

The dependencies field must be provided even if empty.

uv run will search for and use the required Python version. The Python version will download if it is not installed — see the documentation on Python versions for more details.

Improving reproducibility

uv supports an exclude-newer field in the tool.uv section of inline script metadata to limit uv to only considering distributions released before a specific date. This is useful for improving the reproducibility of your script when run at a later point in time.

The date must be specified as an RFC 3339 timestamp (e.g., 2006-12-02T02:07:43Z).

example.py

# /// script
# dependencies = [
#   "requests",
# ]
# [tool.uv]
# exclude-newer = "2023-10-16T00:00:00Z"
# ///

import requests

print(requests.__version__)

Using different Python versions

uv allows arbitrary Python versions to be requested on each script invocation, for example:

example.py

import sys

print(".".join(map(str, sys.version_info[:3])))

$ # Use the default Python version, may differ on your machine
$ uv run example.py
3.12.6

$ # Use a specific Python version
$ uv run --python 3.10 example.py
3.10.15

See the Python version request documentation for more details on requesting Python versions.

Using GUI scripts

On Windows uv will run your script ending with .pyw extension using pythonw:

example.pyw

from tkinter import Tk, ttk

root = Tk()
root.title("uv")
frm = ttk.Frame(root, padding=10)
frm.grid()
ttk.Label(frm, text="Hello World").grid(column=0, row=0)
root.mainloop()

PS> uv run example.pyw

Similarly, it works with dependencies as well:

example_pyqt.pyw

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QGridLayout

app = QApplication(sys.argv)
widget = QWidget()
grid = QGridLayout()

text_label = QLabel()
text_label.setText("Hello World!")
grid.addWidget(text_label)

widget.setLayout(grid)
widget.setGeometry(100, 100, 200, 50)
widget.setWindowTitle("uv")
widget.show()
sys.exit(app.exec_())

PS> uv run --with PyQt5 example_pyqt.pyw

Next steps

To learn more about uv run, see the command reference.

Or, read on to learn how to run and install tools with uv.