set type hint Optional[List[str]], but receive value as ['a,b,c'], not ['a', 'b', 'c']

[shizidushu]

There is the steps:

• app/main.py

from typing import Optional
from fastapi import FastAPI, File, UploadFile, Form

from typing import List

app = FastAPI()

@app.post("/")
async def root(category: Optional[List[str]] = Form(..., title="category"), file: UploadFile = File(..., title="uploaded file")):
    params = locals()
    return {"params": repr(params)}

• Dockerfile

FROM tiangolo/uvicorn-gunicorn-fastapi:python3.8

RUN pip3 install python-multipart

COPY ./app /app

• Build

docker build -t fastapi-test ./

• Run

docker run --rm --name fastapi-test-form -p 8008:80 fastapi-test

• Try

I'd like to get category=['a', 'b', 'c'], but not.
I can't reproduce it when using my windows pc.

[hellocoldworld]

You're passing 'a,b,c' in the same category Form "field". You would need to pass the three letter in three distinct form fields, all of them named 'category'. For example, the following cURL should work

$ curl -X 'POST' \
>   'http://127.0.0.1:8000/' \
>   -H 'accept: application/json' \
>   -H 'Content-Type: multipart/form-data' \
>   -F 'category=a' \
>   -F 'category=b' \
>   -F 'category=c' \
>   -F 'file=@check.html;type=text/html'

[shizidushu]

@hellocoldworld Thanks. I should change the way to send the request.

[tiangolo]

Thanks for the help here @hellocoldworld ! 👏 🙇

Thanks for reporting back and closing the issue @shizidushu 👍

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.