FastAPI 0.65.2 POST request fails with "value is not a valid dict" when using the Requests library; 0.65.1 works (with a caveat)

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First off, thank you for creating this marvellous piece of software. It is a real life-changer.

I hit a very odd bug while implementing some unit tests. Using FastAPI 0.65.2, a POST request via the requests module (requests.post) consistently returns the following error:

{'detail': [{'loc': ['body'], 'msg': 'value is not a valid dict', 'type': 'type_error.dict'}]}

I created a reproducible example:

from fastapi import FastAPI
from pydantic import BaseModel
import uvicorn

app = FastAPI()

class Data(BaseModel):
    field: str


@app.post("/test")
def test_data(data: Data):
    return "Polo"

if __name__=='__main__':
    uvicorn.run(app)

And the requests counterpart:

import requests as rq

def test():
    result = rq.post('http://127.0.0.1:8000/test', data={"field": "Marco"})
    print(f"==[ result: {result.json()}")

if __name__=="__main__":
    test()

The result is

==[ result: {'detail': [{'loc': ['body'], 'msg': 'value is not a valid dict', 'type': 'type_error.dict'}]}

If I downgrade FastAPI to 0.65.1, I still get an error, but a different one:

==[ result: {'detail': [{'loc': ['body', 0], 'msg': 'Expecting value: line 1 column 1 (char 0)', 'type': 'value_error.jsondecode', 'ctx': {'msg': 'Expecting value', 'doc': 'field=heya', 'pos': 0, 'lineno': 1, 'colno': 1}}]}

This can be solved by JSONifying the dictionary:

import requests as rq
import json as js

def test():
    result = rq.post('http://127.0.0.1:8000/test', data = js.dumps({"field": "Marco"}))
    print(f"==[ result: {result.json()}")

if __name__=="__main__":
    test()

Running the above prints

==[ result: Polo

I am slightly perplexed because I am not sure if it is the requests library that is to blame or FastAPI. POSTing via ReDoc works without hiccups with both versions. I am at a loss as to why the second parameter to requests.post is accepted as JSON when it should actually be a dictionary.

Please let me know if I’m missing something obvious or whether I should redirect this to the maintainers of requests. Thank you again for making the lives of developers so much easier.

Cheers!

[Mause]

You probably meant to use the json parameter, not the data parameter. Data is for form data

[thefirebanks]

Can confirm, this still happens! We solved it by adding a -H "Content-Type: application/json" to the curl