Write F#, run Python - a practical guide to Fable.Python

This blog-post is a guide to Fable.Python, written as literate F# that transpiles to Python and generates its own documentation.

1. Introduction - What is Fable.Python and why use it
2. For Python Developers - F# concepts explained for Pythonistas
3. Getting Started - Setup, your first project, hello world
4. Interop - Using existing Python libraries and Fable.Python bindings
5. Bindings - Creating your own type-safe bindings for Python libraries
6. Compatibility - Supported F# features and limitations
7. Async Programming - F# async and Python asyncio
8. Testing - Testing F# code with Python test runners
9. Fable v5 - What's new in Fable v5 for Python
10. Pydantic - Pydantic interop with Decorate and ClassAttributes
11. FastAPI - Building type-safe web APIs with F#
12. Units of Measure - Compile-time dimensional analysis
13. Fable.Literate - The self-documenting converter
14. Summary - Wrap-up, resources, and contributing

This guide is self-documenting: each chapter is an .fs file with embedded Markdown comments. Fable.Literate (the final chapter) processes these files to generate the documentation you're reading - including itself.

The chain:

1. Write F# with embedded Markdown (chapters/*.fs)
2. Compile to Python with Fable
3. Run Fabletext (F# compiled to Python) to extract documentation
4. Output: the Markdown you're reading

The blog post is its own proof of concept.

# Install dependencies
just setup
just restore

# Build everything (F# → Python → Markdown)
just all

# Or generate just the blogpost
just blogpost

just setup      # Install Fable and Python dependencies (uv)
just restore    # Restore NuGet packages
just build      # Compile F# to Python with Fable
just generate   # Convert chapters to individual markdown files
just blogpost   # Generate concatenated blogpost.md for publishing
just format     # Format F# (fantomas) and Python (ruff) files
just lint       # Lint Python (ruff) and Markdown (markdownlint)
just all        # Full pipeline: restore, build, generate, format, lint
just clean      # Remove generated files

chapters/
├── Introduction.fs       # What is Fable.Python
├── Python.fs             # F# for Python developers
├── GettingStarted.fs     # Setup and first project
├── Interop.fs            # Using Python libraries
├── Bindings.fs           # Creating bindings
├── Compatibility.fs      # F# feature support
├── AsyncProgramming.fs   # Async workflows
├── Testing.fs            # Testing with Python
├── FableV5.fs            # What's new in Fable v5
├── Pydantic.fs           # Pydantic interop
├── UnitsOfMeasure.fs     # Dimensional analysis
├── FableLiterate.fs      # Symlink → ../Fable.Literate/App.fs
└── Summary.fs            # Wrap-up and resources
Fable.Literate/
├── App.fs                # Fable.Literate converter (F#)
└── Fable.Literate.fsproj
output/
├── chapters/             # Generated Python from chapters
└── Fable.Literate/
    └── app.py            # Generated converter (Python)
docs/
├── Introduction.md       # Individual chapter docs
├── Python.md
├── ...
└── blogpost.md           # Concatenated for Hashnode

Defined in justfile:

chapters := "Introduction Python GettingStarted Interop Bindings Compatibility AsyncProgramming Testing FableV5 Pydantic UnitsOfMeasure FableLiterate Summary"

To add a new chapter, just add the file and update this list.

• Fable 5 (alpha) - F# to Python compiler
• uv - Python dependency management
• just - Command runner
• ruff - Python formatter/linter
• fantomas - F# formatter
• markdownlint - Markdown linter

• Thoth.Json.Python - Type-safe JSON
• AsyncRx - Reactive extensions
• Fable.Giraffe - Web framework
• Feliz.ViewEngine - HTML DSL
• Siren - Mermaid diagrams
• Fable.Pyxpecto - Testing
• ARCtrl - Real-world multi-target library

• Fable
• Fable.Python Documentation
• Fable.Python GitHub
• BINDINGS_GUIDE.md - Comprehensive binding patterns

Part of F# Advent 2025