Python FastAPI: Uploading Text file gives internal server error

Question

I'm using FastAPI to write an API to upload text files and to read the txt file contents.

@app.post('/read_txt_file', response_class=PlainTextResponse)
async def upload_file_and_read(file: UploadFile = File(...)
                      , fileExtension: str = Form(...)):
 
    if(fileExtension == 'txt'):
        raw_txt = readTxt(file)
        raw_txt = raw_txt.decode()

    return raw_txt


def readTxt(file):
    return file.read()

This code above throws internal server error. Can I know how to correct it?

Logs:

File "/home/readerProject/.venv/lib/python3.7/site-packages/fastapi/routing.py", line 183, in app dependant=dependant, values=values, is_coroutine=is_coroutine File "/home/readerProject/.venv/lib/python3.7/site-packages/fastapi/routing.py", line 133, in run_endpoint_function return await dependant.call(**values)

File "/home/readerProject/api.py", line 28, in upload_file_and_read raw_txt = raw_txt.decode()

AttributeError: 'coroutine' object has no attribute 'decode' /home/readerProject/.venv/lib/python3.7/site-packages/uvicorn/protocols/http/h11_impl.py:396: RuntimeWarning: coroutine 'UploadFile.read' was never awaited
self.transport.close() RuntimeWarning: Enable tracemalloc to get the object allocation traceback

raw_txt = await raw_txt.decode() instead of raw_txt = raw_txt.decode() ? — JPG
– JPG, Commented Oct 15, 2020 at 7:58
why do we need await ? most importantly when do we have to use await ? — Gissipi_453
– Gissipi_453, Commented Oct 15, 2020 at 8:00
You are using a coroutine so you definitely need to use await like @ArakkalAbu mentioned, since it is not a function and you can't directly return it, See PEP 492 — Yagiz Degirmenci
– Yagiz Degirmenci, Commented Oct 15, 2020 at 8:04

JPG · Accepted Answer · 2020-10-15 08:17:35Z

3

You have to call the readTxt(...) function with await syntax as

raw_txt = await readTxt(file)
         ^^^^^^^

Minimal verifiable example

from fastapi import FastAPI, UploadFile, File

app = FastAPI()


@app.post('/read_txt_file')
async def upload_file_and_read(
        file: UploadFile = File(...),
):
    if file.content_type.startswith("text"):
        text_binary = await readTxt(file) # call `await`
        response = text_binary.decode()
    else:
        # do something
        response = file.filename

    return response


def readTxt(file):
    return file.read()

As a side note, you can retrieve the context type by inspecting the file.content_type which can be used to identify the file extension.

answered Oct 15, 2020 at 8:17

JPG

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