Python Workers: FastMCP Example

This is an example of a Python Worker that uses the FastMCP package.

>[!NOTE]
>Due to the size of the Worker, this example can only be deployed if you're using the Workers Paid plan. Free plan users will encounter deployment errors because this Worker exceeds the 3MB size limit.

Adding Packages

Vendored packages are added to your source files and need to be installed in a special manner. The Python Workers team plans to make this process automatic in the future, but for now, manual steps need to be taken.

Vendoring Packages

First, install Python3.12 and pip for Python 3.12.

Currently, other versions of Python will not work - use 3.12!

Then create a virtual environment and activate it from your shell:

python3.12 -m venv .venv

source .venv/bin/activate

Within our virtual environment, install the pyodide CLI:

.venv/bin/pip install pyodide-build

.venv/bin/pyodide venv .venv-pyodide

Lastly, download the vendored packages. For any additional packages, re-run this command.

.venv-pyodide/bin/pip install -t src/vendor -r vendor.txt

Developing and Deploying

To develop your Worker, run npx wrangler@latest dev.

To deploy your Worker, run npx wrangler@latest deploy.

Testing

To test run:

source .venv/bin/activate

pip install -r requirements-test.txt

pytest tests

Linting and Formatting

This project uses Ruff for linting and formatting:

pip install ruff
ruff check .  # Run linting
ruff format .  # Format code