FastAPI 0.68.0 Breaks Usage of tuple in Input / Output compared to 0.67.0

First Check

• I added a very descriptive title to this issue.
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• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

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Example Code

# main.py

import uvicorn
from fastapi import FastAPI, Form

app = FastAPI()

@app.post("/")
def hello(arg: tuple[int, int] = Form(...)) -> str:
    pass

if __name__ == "__main__":
    uvicorn.run("main:app", port=8080)

Description

1. Run pip install uvicorn fastapi==0.68.0.
2. Run python ./main.py
3. Hit localhost:8080/docs, observe internal server error with below validation errors:

pydantic.error_wrappers.ValidationError: 2 validation errors for OpenAPI
components -> schemas -> Body_hello__post -> properties -> arg -> items
  value is not a valid dict (type=type_error.dict)
components -> schemas -> Body_hello__post -> $ref
  field required (type=value_error.missing)

1. Run pip install fastapi==0.67.0
2. Hit localhost:8080/docs, observe that endpoint documentation is successfully generated.

Operating System

Linux

Operating System Details

Ubuntu 20.04

FastAPI Version

0.68.0 has bug, 0.67.0 does not have bug.

Python Version

3.9

Additional Context

Any use of tuple in an input (Form, and BaseModel as JSON) or output (BaseModel as JSON) results in above error.

[elrik75]

According to this: https://stackoverflow.com/questions/57464633/how-to-define-a-json-array-with-concrete-item-definition-for-every-index-i-e-a it’s possible to have tuples in openapi3.1.

It could be great if @tiangolo could tell us if FastAPI will support Tuples again or if we need adapt our APIs. For now we are stuck in 0.67

[tiangolo]

Thanks for the discussion everyone! This should be solved by https://github.com/tiangolo/fastapi/pull/3874

It is available in FastAPI 0.73.0, released in the next hours. 🎉

For more context, check the last comment there: https://github.com/tiangolo/fastapi/pull/3874#issuecomment-1019578028

---

In short, using tuples now won’t break the rest of Swagger UI.

And although they are supported by OpenAPI 3.1.0, Swagger UI doesn’t support OpenAPI 3.1.0 yet. Even though FastAPI already has a couple of corner cases where it is more compatible with 3.1.0, I can’t change the generated version yet, as Swagger UI wouldn’t render it at all.

So, you can continue using tuples with FastAPI 0.73.0, those tuples won’t always be properly rendered in Swagger UI (as they have never been), but now that won’t break the rest of Swagger UI, and you will get the proper validation, etc. 🎉