Let's set up a Fable.Python project from scratch and get our first F# code running as Python.

You'll need:

• .NET SDK (6.0 or later)
• Python 3.12+ (Fable targets Python 3.12 or higher)

Create a new directory and initialize an F# project:

mkdir my-fable-python
cd my-fable-python

# Create F# console app
dotnet new console -lang F#

# Set up local tools and install Fable 5 (alpha)
dotnet new tool-manifest
dotnet tool install fable --version 5.0.0-alpha.20

# Add Fable.Core package
dotnet add package Fable.Core --version 5.0.0-beta.4

Fable-generated Python code requires the fable-library runtime:

pip install "fable-library==5.0.0a20"

Note: Version pinning matters. The fable-library version must match your Fable compiler version. PyPI uses 5.0.0a20 format instead of 5.0.0-alpha.20.

Replace the contents of Program.fs with:

printfn "Hello from Fable.Python!"

let square x = x * x
let numbers = [1; 2; 3; 4; 5]
let squares = numbers |> List.map square

printfn "Squares: %A" squares

Transpile to Python:

dotnet fable --lang python

This creates Program.py in your project directory. Run it:

python3 Program.py

You should see:

Hello from Fable.Python!
Squares: [1; 4; 9; 16; 25]

For development, use watch mode to automatically recompile on changes:

dotnet fable watch --lang python

Now any changes to your F# files will instantly produce updated Python output.

After setup, your project looks like this:

my-fable-python/
├── Program.fs          # Your F# source code
├── Program.py          # Generated Python (don't edit!)
├── my-fable-python.fsproj
├── fable_modules/      # Fable runtime modules
└── .config/
    └── dotnet-tools.json

Now that you have a working setup, let's explore how to interact with Python libraries in the next chapter on Bindings.