python
package management
uv
I’m using uv to manage python versions and per-project virtual environments.
uvx/uv tool
One interesting feature of uv is the ability to run tools without installing
them, e.g. uvx ruff (which is just an alias for uv tool run ruff) to run the
code format without requiring it in the project. This will install the tool into
a temporary, isolated environment and then run it. Note that this workflow
therefore requires an internet connection, and does not work offline. Instead we
can run uv tool install ruff to remove the need to re-install the tool every
time we run it. The tool should then be visible in the PATH, but its modules
will not be available for use in the project.
scripts (uv run)
We can run one-off scripts (outside of a project) with uv run as long as we
specify the dependencies explicitly. For example,
1uv run --with "requests<3, pandas[pyarrow]" script.py
will temporarily install the specified dependencies and run the script in that temporary environment. This is convenient for those one-off scripts that you don’t necessarily want to make a new directory, etc. etc. As PEP 723 notes:
Python is routinely used as a scripting language, with Python scripts as a (better) alternative to shell scripts, batch files, etc. When Python code is structured as a script, it is usually stored as a single file and does not expect the availability of any other local code that may be used for imports. As such, it is possible to share with others over arbitrary text-based means such as email, a URL to the script, or even a chat window. Code that is structured like this may live as a single file forever, never becoming a full-fledged project with its own directory and pyproject.toml file.
The ergonomics of running scripts with a lengthy list of requirements is not
great, but uv is able to take advantage of the metadata specification
proposed by PEP 723 to use requirements specified in the script itself. This
looks something like
1# /// script
2# requires-python = ">=3.13"
3# dependencies = [
4# "pandas[pyarrow]",
5# "requests<3",
6# ]
7# ///
You don’t need to write this by hand – uv can do it for you:
1uv add --script script.py "requests<3" "pandas[pyarrow]"