This is a short guide on how to upgrade a project from using pip with a requirements.txt file to using Astral's uv. It assumes that uv is already installed and that you have a project set up with a requirements.txt file.

Initialize uv:

uv init

Remove hello.py.

rm hello.py

Modify project.toml to update the information about the project.

Add the dependencies from requirements.txt to the project.toml file:

uv add -r requirements.txt

That's it! You can now use uv to manage your dependencies. You can run the project with:

uv run your_script.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
python your_script.py

To add new dependencies, you can use the uv add command:

uv add package_name

To upgrade a package, you can use the uv upgrade command:

uv lock --upgrade-package package_name

I wanted to run a Python tool without installing it, or preparing a virtual environment and all that. This is now very easy with uv, using uvx.

I wanted to run markitdown, a tool to convert various files to Markdown. I didn't want to install it, so I used uvx:

uvx markitdown "file_to_convert.docx" > output_file.md

It downloads the tool and installs it in a temporary, isolated environment.

A tool can be installed with uv tool install, like this:

uv tool install markitdown

It's very convenient.

I was trying to serve a JavaScript file with Python's http.server module, but I was getting this error:

Loading module from “http://localhost:9876/main.js” was blocked because of a disallowed MIME type (“text/plain”).

I saw in this StackOverflow answer that I needed to change the MIME type for JavaScript files. I'm using Windows, so I checked the key HKEY_CLASSES_ROOT\.js in RegEdit, and I found that it had this value:

(Default)     JSFile
ContentType   text/plain
PerceivedType text

I changed the ContentType to application/javascript, and now my JavaScript files are served with the correct MIME type.

I'm not sure why the MIME type was set to text/plain in the first place. I'm guessing that it was set by a program that I installed, but I don't know which one. I'm also not sure if changing the MIME type will cause any problems with other programs.

The other day, I wrote a post about how I fixed a problem with Pylance not finding a local import. It worked, but now mypy was complaining about the same import.

The solution was installing the package in compat mode with:

pip install -e . --config-settings editable_mode=compat

I have a Python package called cloudmodel that uses Pint to define units and adds some to the default registry. When I read a pickle file that use these units, I get an error:

int.errors.UndefinedUnitError: 'usd' is not defined in the unit registry

The way to fix it is to set the application registry to the one used by cloudmodel:

from cloudmodel.unified.units import ureg
from pint import set_application_registry

set_application_registry(ureg)