[Python] POST request to FastAPI using Python Requests with a file and query parameters

I am using FastAPI to serve some ML models and I have a Streamlit basic UI using Python Requests module.

One of my service is getting an image through a POST request and it is working like a charm.

Server side

@app.post("/segformer")
async def segformer(file: Optional[UploadFile] = None):


curl given by {BASE_URI}/docs

curl -X 'POST' \
'http://localhost:8080/segformer' \
-H 'accept: application/json' \
-H 'Content-Type: multipart/form-data' \
-F 'file=@image1.jpg;type=image/jpeg'


Client side using Python Requests

response = requests.post(f"{BASE_URI}/segformer", files=files)


As soon as I want to add additional parameters, it gets creepy. For example:

Server side

@dataclass
class ModelInterface:
model_name: str = "detr"
tags: List[str] = Query(...)

@app.post("/detr")
async def detr(file: UploadFile = File(...), model: ModelInterface = Depends()):


curl -- given by {BASE_URI}/docs

curl -X 'POST' \
'http://localhost:8080/detr?model_name=detr&tags=balloon&tags=dog' \
-H 'accept: application/json' \
-H 'Content-Type: multipart/form-data' \
-F 'file=@image1.jpg;type=image/jpeg'


Until that point everything works fine. Once I want to convert that call using Python Requests, I have some issues, which always end up in /detr HTTP/1.1" 400 Bad Request error.

Here is what I've tried:

Client side using Python Requests

headers = {
"Content-type": "multipart/form-data",
"accept": "application/json"
}

payload = {
"tags": ["balloon", "dog"]
}

response = requests.post(
f"{BASE_URI}/detr",
headers=headers,
json=payload, <- also *data*
files=files,
)


At the end it seems that the problem narrows on how to convert this:

curl -X 'POST' \
'http://localhost:8080/detr?tags=balloon&tags=dog' \
-H 'accept: application/json' \
-H 'Content-Type: multipart/form-data' \
-F 'file=@image1.jpg;type=image/jpeg'


to a valid Python Requests call!

I also faced the issue that the following FastAPI code:

@dataclass
class ModelInterface:
model_name: str = "detr"
tags: List[str] = None

@app.post("/detr2")
async def detr2(file: UploadFile = File(...), model: ModelInterface = Form(...)):
...


translates to this curl command:

curl -X 'POST' \
'http://localhost:8080/detr2' \
-H 'accept: application/json' \
-H 'Content-Type: multipart/form-data' \
-F 'file=@image1.jpg;type=image/jpeg' \
-F 'model={
"model_name": "detr",
"tags": [
"balloon", "dog"
]
}'


which fails with a "POST /detr2 HTTP/1.1" 422 Unprocessable Entity error

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