https://github.com/jvllmr/fastapi-deferred-init

Improve start-up time for FastAPI apps with many nested routers
https://github.com/jvllmr/fastapi-deferred-init

fastapi speedup

Last synced: 5 months ago
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Improve start-up time for FastAPI apps with many nested routers

• Host: GitHub
• URL: https://github.com/jvllmr/fastapi-deferred-init
• Owner: jvllmr
• License: mit
• Created: 2023-10-21T21:18:41.000Z (over 2 years ago)
• Default Branch: master
• Last Pushed: 2025-04-01T06:11:27.000Z (about 1 year ago)
• Last Synced: 2025-04-01T07:24:08.388Z (about 1 year ago)
• Topics: fastapi, speedup
• Language: Python
• Homepage: https://jvllmr.github.io/fastapi-deferred-init/dev/bench/
• Size: 291 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# fastapi-deferred-init

![PyPI - Downloads](https://img.shields.io/pypi/dd/fastapi-deferred-init)

[![GitHub license](https://img.shields.io/github/license/jvllmr/fastapi-deferred-init)](https://github.com/jvllmr/fastapi-deferred-init/blob/master/LICENSE)

![Tests](https://github.com/jvllmr/fastapi-deferred-init/actions/workflows/test.yml/badge.svg)

## The Problem

When using nested routers in a FastAPI project its start-up time can get long quite fast.

That is because every router re-calculates the routes defined by a nested router when including it and the pre-calculated values by the nested router never get used. In short: values in nested routers are calculated although they will never be used.

## The Solution

This library provides a modified APIRoute that defers the calculation of values to the first actual attribute access. A router which uses the route as a default is also provided.

## Caveat

When using the deferred APIRoute on every layer of the app, startup errors are deferred to the first time a route is called. So errors related to route registration might go undetected if the route is not tested at least once.

## Pull Request

I created a pull request to merge this change back into FastAPI: https://github.com/tiangolo/fastapi/pull/10589