Question: Running into an error that has started after a reboot. I am testing using Azure Functions in conjunction with FastAPI based on: https://dev.to/manukanne/azure-functions-and-fastapi-14b6 Code was operating and test API call worked as expected. After a reboot of the machine and restarting VSCode I am now running into an issue when attempting to run locally. I worked through SO: 76842742 which is slightly different setup but similar type of error being seen. Virtual environment is running as expected and requirements.txt showing installed. Have run with verbose flag as well but no additional error messages were provided. Current error: Worker failed to index functions Result: Failure Exception: ValueError: Could not find top level function app instances in function_app.py. My function.json has the scriptFile: init.py which I thought would need to be function_app.py but the error indicates it is looking for the function_app.py regardless. I created a copy of my function_app.py and named it "__init __.py" as a potential fix but that produced the same error code. At this point I am at a loss as to why the index function is not being found. Any thoughts around a potential solution? Found Python version 3.11.0 (py) Core Tools Version: 4.0.5611 VS Code: 1.88.1 function_app.py import azure.functions as func from fastapi import FastAPI, Request from fastapi.responses import JSONResponse import logging app = FastAPI() @app.exception_handler(Exception) async def handle_exception(request: Request, exc: Exception): return JSONResponse( status_code=400, content={"message": str(exc)}, ) @app.get("/") async def home(): return { "info": "Try the API path for success" } @app.get("/v1/test/{test}") async def get_test( test: str,): return { "test": test, } def main(req: func.HttpRequest, context: func.Context) -> func.HttpResponse: return func.AsgiMiddleware(app).handle_async(req, context)  function.json { "scriptFile": "__init__.py", "bindings": [ { "authLevel": "function", "type": "httpTrigger", "direction": "in", "name": "req", "methods": [ "get", "post" ], "route": "/{*route}" }, { "type": "http", "direction": "out", "name": "$return" } ] }  ADDITIONAL ADD host.json { "$schema": "https://raw.githubusercontent.com/Azure/azure-functions-host/dev/schemas/json/host.json", "version": "2.0", "logging": { "applicationInsights": { "samplingSettings": { "isEnabled": true, "excludedTypes": "Request" } } }, "extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.*, 5.0.0)" }, "extensions": { "http": { "routePrefix": "" } } } 

Answer: Based on comments by JarroVGIT, I refactored the function_app.py code to: import azure.functions as func from fastapi import FastAPI, Request, Response import logging fast_app = FastAPI() @fast_app.exception_handler(Exception) async def handle_exception(request: Request, exc: Exception): return Response( status_code=400, content={"message": str(exc)}, ) @fast_app.get("/") async def home(): return { "info": "Try the API path for success" } @fast_app.get("/v1/test/{test}") async def get_test( test: str,): return { "test": test, } app = func.AsgiFunctionApp(app=fast_app, http_auth_level=func.AuthLevel.ANONYMOUS,)  Removing the def main and adding the app call. This has resolved the issue and allows the azure function to start normally.