Does FastAPI have to pin starlette?

[dimaqq]

First Check

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Example Code

from fastapi.testclient import TestClient

TestClient(app, headers={...})

Description

FastAPI re-exports starlette TestClient which seems to be an httpx.Client connected to the asgi app under test.

starlette has recently fixed the TestClient.__init__ to follow httpx.Client.__init__ so that the earlier accepts headers=... kwarg, just like the latter.

Kludex/starlette#1966

starlette has made a release 0.23.0, but the latest FastAPI pins a specific version starlette==0.22.0

Thus, as a dev, I can't use the latest "features" or more like reasonable expectations for the TestClient.

A newcomer would read the docs / source code and would expect TestClient to accept headers kwarg and get confused why that's rejected.

Thus, the question: is there a reason to pin a specific version of starlette?

Operating System

Other

Operating System Details

An issue with any OS.

FastAPI Version

0.88.0

Python Version

3.10, etc.

Additional Context

No response

[jgould22]

FastAPI is integrated quite closely with starlette, and unfortunately starlette doesn't use semantic versioning, so it's easy for a breaking starlette change to break FastAPI. The latest version of starlette does this, for example

#2532

If Starlette released a change that FastAPI did not support and you did not pin the version every install would break and cause everyone to have to pin starlette which is not desirable.

Generally in library(which fastapi is) code you should pin your dependencies, or use a lock file to ensure that the library is getting a version of its dependencies that it is known to support. For a library having known working code for a specific version is more important than features.

[dimaqq]

I guess as long as both FastAPI and Starlette are in the 0.x.x series, we just have to live with that.

P.S. I kinda wish that FastAPI at least would graduate, because SemVer has a gotcha for 0.x.x that most devs are not aware of. At least I was not and my peers were not.