Adding async to Fastapi function gives me the "'coroutine' object is not iterable" error [duplicate]

Question

Why does adding async to Fastapi function gives me the "'coroutine' object is not iterable" error

I only get the error after I add the async keyword at the front of my function as follows, when I call the function/endpoint using Swagger UI:

@router.post("/create")
async def job_create_post_view(
    request: Request, 
    is_htmx=Depends(is_htmx), 
    db:Session=Depends(get_db),
    short_description: str = Form(default=None),
    long_description: str = Form(default=None),
   
   .....
    
    job_image:Optional[UploadFile]=File(...)
    ):
    

The error is as follows:

[TypeError("'coroutine' object is not iterable"), TypeError('vars() argument must have __dict__ attribute')]

I am trying to do something asynchronous inside the function:

contents = await job_image.read()

This is the stack trace:

Traceback (most recent call last):
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 366, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\uvicorn\middleware\proxy_headers.py", line 75, in __call__
    return await self.app(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\applications.py", line 269, in __call__
    await super().__call__(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\applications.py", line 124, in __call__
    await self.middleware_stack(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\middleware\errors.py", line 184, in __call__
    raise exc
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\middleware\errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\middleware\cors.py", line 92, in __call__
    await self.simple_response(scope, receive, send, request_headers=headers)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\middleware\cors.py", line 147, in simple_response
    await self.app(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\middleware\authentication.py", line 48, in __call__
    await self.app(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\exceptions.py", line 93, in __call__
    raise exc
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\exceptions.py", line 82, in __call__
    await self.app(scope, receive, sender)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\middleware\asyncexitstack.py", line 21, in __call__
    raise e
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\middleware\asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\routing.py", line 670, in __call__
    await route.handle(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\routing.py", line 266, in handle
    await self.app(scope, receive, send)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\starlette\routing.py", line 65, in app
    response = await func(request)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\routing.py", line 235, in app
    response_data = await serialize_response(
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\routing.py", line 149, in serialize_response
    return jsonable_encoder(response_content)
  File "D:\TEMP\job_search - revert\venv\lib\site-packages\fastapi\encoders.py", line 144, in jsonable_encoder
    raise ValueError(errors)
ValueError: [TypeError("'coroutine' object is not iterable"), TypeError('vars() argument must have __dict__ attribute')]

Answer 1

I had the same error.
I found out that the problem was from calling a async function without putting await before calling it.

The function which I was trying to call, was like something like this:

async def func1():
    ...

async def func2():
    x = func1()
    ...

So, the problem got resolved when I edited like this:

async def func1():
    ...

async def func2():
    x = await func1()
    ...

Answer 2

[TypeError("'coroutine' object is not iterable"), TypeError('vars() argument must have __dict__ attribute')] usually happened when the developer made a mistake inside the async function like this [Mistake]:

@app.get("/")
 async def read_root():
    return fetch_all_todos()

but the correct behavior for async is like this [Correct]:

@app.get("/")
async def read_root():
    response = await fetch_all_todos()
    return response

You need to put await in a variable and then return it.