👀 Views: 58 💬 Answers: 1 📅 Created: 2025-06-22

fastapi asyncio httpx Python

I'm stuck on something that should probably be simple. I am working on a FastAPI application, and I have a situation where I'm trying to populate a dictionary asynchronously with data fetched from an external API. However, when I try to access the dictionary after the asynchronous calls, it appears to be empty. I suspect it has to do with the timing of the async functions and how I'm managing the state of the dictionary. Here’s a simplified version of my code: ```python import asyncio from fastapi import FastAPI import httpx app = FastAPI() my_data_dict = {} async def fetch_data(key): async with httpx.AsyncClient() as client: response = await client.get(f'http://example.com/api/data/{key}') my_data_dict[key] = response.json() async def populate_dict(keys): tasks = [fetch_data(key) for key in keys] await asyncio.gather(*tasks) @app.on_event('startup') async def startup_event(): await populate_dict(['key1', 'key2', 'key3']) @app.get('/data') def get_data(): return my_data_dict ``` When I start the FastAPI server and go to the `/data` endpoint, I get an empty dictionary `{}` instead of the expected populated data. I confirmed that the API calls succeed and return valid responses; however, they do not seem to populate `my_data_dict` as expected. Additionally, I am not seeing any behavior messages in the console. I have tried adding `print(my_data_dict)` statements after the async calls, but it still shows as empty when accessed in the `get_data` function. I suspect this might be a scope scenario or a timing scenario with the async calls. Is there a best practice for managing the state of dictionaries when using async functions in FastAPI? Any help would be greatly appreciated! I'm developing on Debian with Python. What's the correct way to implement this?