---
title: "One Core, Two Interfaces, No Rewrites"
url: https://daily.dev/posts/one-core-two-interfaces-no-rewrites-g1a1au956
source_url: https://belderbos.dev/blog/two-interfaces-one-core
type: article
source: "Planet Python"
published: 2026-07-04T19:52:57.679Z
updated: 2026-07-05T14:20:54.374Z
tags: ["python", "architecture", "vector-search", "fastapi"]
reading_time: 6
upvotes: 2
comments: 0
language: en
---

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# One Core, Two Interfaces, No Rewrites

**[Planet Python](https://daily.dev/sources/planetpython)** · 6 min read · 2 upvotes · 0 comments

## Summary

A walkthrough of building a shared functional core that powers both a CLI and a FastAPI web app without duplicating logic. Key patterns covered include pure functions as the shared spine, using Python's `@cache` decorator for memoized library loading, FastAPI's `lifespan` context for pre-warming the vector matrix and PyTorch model before the first request, and lazy imports to ensure Hugging Face offline environment variables are set before `sentence-transformers` loads. The post argues that classes are unnecessary here — NamedTuples and memoized functions handle all state — and that adding a third interface later requires only importing the same core functions.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://belderbos.dev/blog/two-interfaces-one-core>

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---

Tags: [#python](https://daily.dev/tags/python), [#architecture](https://daily.dev/tags/architecture), [#vector-search](https://daily.dev/tags/vector-search), [#fastapi](https://daily.dev/tags/fastapi)

[View this post on daily.dev](https://daily.dev/posts/one-core-two-interfaces-no-rewrites-g1a1au956)