validation errors for openAPI schema with length >=2 tuples

[dconathan]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• 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.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from typing import Tuple
from fastapi import FastAPI
from pydantic import BaseModel


class FooArgs(BaseModel):
    bars: Tuple[str, str]


app = FastAPI()


@app.post("/foo")
def foo(args: FooArgs):
    ...

Description

If you try to retrieve the /openapi.json, the FooArgs get a validation error:

  File ".../lib/python3.9/site-packages/fastapi/openapi/utils.py", line 410, in get_openapi
    return jsonable_encoder(OpenAPI(**output), by_alias=True, exclude_none=True)  # type: ignore
  File "pydantic/main.py", line 406, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 2 validation errors for OpenAPI
components -> schemas -> FooArgs -> properties -> bars -> items
  value is not a valid dict (type=type_error.dict)
components -> schemas -> FooArgs -> $ref
  field required (type=value_error.missing)

This error is new to fastapi>=0.68, it does not happen with fastapi==0.67.0.

I think this is related to Pydantic coercing Tuple[str, str] into Dict[str, str] somewhere?

Things that don't cause this error:

class FooArgs(BaseModel):
    bars: Tuple[str]

class FooArgs(BaseModel):
    bars: Tuple[str, ...]

This that do cause this error:

class FooArgs(BaseModel):
    bars: Tuple[str, str]

class FooArgs(BaseModel):
    bars: Tuple[int, str]

class FooArgs(BaseModel):
    bars: Tuple[str, str, str]  # etc.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.68.1

Python Version

3.9.1 (also seeing this in 3.8.*)

Additional Context

Seems pretty likely that this commit introduced it, but there's a lot going on so I'm not sure where:

97fa743#diff-4939896f79697822446463d5d6dfbf7a0ea5805c46565d355c7305d86f3405c7

[trevorwang]

Tested your code on fastapi 0.68.1 with python 3.8. works pretty well.

class FooArgs(BaseModel):
    bars: Tuple[str, str]


@app.post("/foo")
def foo(args: FooArgs):
    pass

[dconathan]

Where is that screenshot from? Are you able to curl http://127.0.0.1:8000/openapi.json ?

$ cat app.py
from typing import List, Tuple
from fastapi import FastAPI
from pydantic import BaseModel


class FooArgs(BaseModel):
    bars: Tuple[str, str]

app = FastAPI()


@app.post("/foo")
def foo(args: FooArgs):
    ...

$ uvicorn app:app
INFO:     Started server process [72531]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:49438 - "GET /openapi.json HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application

... (same error as above)

$ curl http://localhost:8000/openapi.json
Internal Server Error

If it matters, I'm on:

$ pip freeze | grep pydantic
pydantic==1.8.2

[trevorwang]

it's http://localhost:8000/docs

It is not working now. I got the same error as yours. Sad.

[fakegermano]

Can confirm had the same errors here, docs work on previous versions, but update seems to break something.

After a bit of search, I found an issue in pydantic related to this:

pydantic/pydantic#3210

[fakegermano]

after another bit of search, I think this issue is a duplicate of both #3665 and #3782, there is also some more info there!

[tiangolo]

It seems this is a duplicate of #3665

In short, it should be fixed by FastAPI 0.73.0, released in the next hours. 🎉

For more info, read the last comment in that issue: #3665 (comment)

And the comment in the PR: #3874 (comment)

[github-actions]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.