# Flexible Python Version Management with uv and tox

When working with Python projects that use [tox](https://pydevtools.com/handbook/reference/tox.md) for testing, you may encounter version mismatch errors like:

```console
lint-format: skipped because could not find python interpreter with spec(s): python3.8
```

This happens when tox expects a specific Python version that isn't available in your environment. Traditionally, this would require:

1. Installing the required Python version
2. Creating a new virtualenv
3. Reinstalling dependencies
4. Running tox again

However, [uv](https://pydevtools.com/handbook/reference/uv.md) provides a more elegant solution through its tool isolation feature. By using [`uvx`](https://pydevtools.com/handbook/reference/uvx.md) with the `--python` flag, you can run tox with any Python version on demand:

```console
$ uvx --python 3.8 tox -e lint
```

{{< callout type="info" >}}
uvx creates an isolated environment with the specified Python version just for this command execution, leaving your project's environment untouched.

uv also \_automatically installs\_ Python 3.8 if you don't have it available on your system.
{{< /callout >}}

This approach offers several advantages:

* No need to manage multiple virtualenvs
* Works with any Python version uv can access
* Maintains isolation between environments
* Zero configuration required

## Learn More

* [How to use uv to speed up tox](https://pydevtools.com/handbook/how-to/how-to-use-uv-to-speed-up-tox.md)
* [tox-uv reference](https://pydevtools.com/handbook/reference/tox-uv.md)