Design, Generate, Deploy: Contract-First with FastAPI

🔊 Recorded at PyCon DE & PyData 2025, April 24, 2025 https://2025.pycon.de/program/ZACM3E/ 🎓 A practical exploration of contract-first API development using FastAPI and OpenAPI Generator, demonstrating how to improve cross-team collaboration and reduce implementation bugs. Speakers: Dr. Evelyne Groen, Kateryna Budzyak Description: This presentation explores the contract-first approach to API development using FastAPI and OpenAPI specifications. Dr. Groen and Budzyak demonstrate how this methodology improves collaboration between data science and backend engineering teams at Malt, a European freelancer marketplace. The speakers contrast traditional code-first development with contract-first approaches, highlighting how starting with OpenAPI specifications as a single source of truth can streamline API development and reduce implementation errors. The presentation details the practical implementation using OpenAPI Generator to automatically generate endpoints and data models from specifications, including the integration of Pydantic for data validation. The speakers address technical challenges such as template customization and maintaining synchronization between client and server implementations through continuous deployment pipelines. While acknowledging some limitations of the OpenAPI Generator's beta status and the learning curve associated with tools like Mustache templating, the presenters emphasize how this approach standardizes application structure, reduces coding overhead, and facilitates clearer communication between teams. The methodology particularly benefits organizations managing complex API interactions between different programming environments, such as Python-based data science services and Kotlin-based backend systems. ⭐️ About PyCon DE & PyData: The PyCon DE & PyData conference unite the Python, AI, and data science communities, offering a unique platform for collaboration and innovation. The PyCon DE & PyData 2025 conference, provided an exceptional experience, fostering deeper connections within the Python community while showcasing advancements in AI and data science. Attendees enjoyed a diverse and engaging program, solidifying the event as a highlight for Python and AI enthusiasts nationwide. Follow us: • LinkedIn: https://www.linkedin.com/company/28908640/ • X: https://www.x.com/pyconde Links: • Conference website: http://pycon.de • Other sessions: https://2025.pycon.de/talks/ The conference is organized by • Python Softwareverband e.V.: http://pysv.org • NumFOCUS Inc.: http://numfocus.org • Pioneers Hub gemeinnützige GmbH: http://pioneershub.org If you enjoyed this session, please like, comment, and subscribe to our channel for more insightful talks and discussions. Share this video with your network to spread the knowledge! Hashtags: #Python #PyConDE #PyData #OpenSource #AI #DataScience #MachineLearning #SoftwareDevelopment #LLMs #Community Acknowledgements: Special thanks to all the volunteers and sponsors who made this event possible. About: Python Softwareverband e.V.: PySV is a non-profit that promotes the use and development of Python in Germany through events, education, and advocacy, fostering an open Python community. NumFOCUS Inc. supports open-source scientific computing by providing financial and logistical support to key projects like NumPy and Jupyter, promoting sustainable development and collaboration. Pioneers Hub gemeinnützige GmbH: is a non-profit fostering innovation in AI and tech by connecting experts and promoting knowledge exchange through events and collaborative initiatives.