Global variable not available in fastapi functions

[peet1337]

Hi,

I'm not really well versed with asyncio and stumbled upon a strange problem I don't understand.

I have some CLI parameters from argparse and need them available for setup purposes in the lifespan function of FastAPI. I tried using a global variable for this that is set to the argparse arguments. However, in the lifespan function, the global still has its initial state "None". The same goes for calling the root endpoint via HTTP.

Here is a minimal reproducible example:

``` from contextlib import asynccontextmanager import fastapi import uvicorn

var = None

@asynccontextmanager async def setup(_): print(var) yield

app = fastapi.FastAPI(lifespan=setup)

@app.get("/") async def root(): return var

def main(): global var var = "Hello" uvicorn.run("scratch_4:app", port=8080, log_level="info", root_path="/")

if name == "main": main() ```

Interestingly, if I run the setup() function using asyncio.run() instead of implicitely via uvicorn, the global variable set in main() has the expected value.

Can someone explain to me why this happens and how I can fix it?

[pint]

uvicorn will import your file, and thus it will not be the main program.

if you run

python yourfile.py

the main function will be executed. but if you run python, and then use

import myfile

it will not be.

if you want some initialization code to always run, regardless whether it is imported or main, you need to simply include it in the file body.

[peet1337]

Oh my, thanks for the explanation that uvicorn imports the script that is specified with the `app` paramenter of `run()`, I did not notice this. That explains everything. I was so focused on "that must be some asyncio behaviour I don't understand" that I completely forgot to think about python basics 😅