Startup and shutdown events in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when the FastAPI app starts?

Consider this FastAPI app with a startup event handler. What will be printed to the console when the app starts?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.on_event("startup")
async def startup_event():
    print("App is starting")

@app.get("/")
async def read_root():
    return {"message": "Hello"}

A Nothing is printed until the first request is received

B The app raises an error because startup events must be synchronous

C The message 'App is starting' is printed every time a request is received

D The message 'App is starting' is printed once when the app starts

💡 Hint

Think about when startup events run in FastAPI lifecycle.

Startup event handlers run once when the app starts, before handling any requests. They can be async functions.

❓ component_behavior

intermediate

What happens on app shutdown with multiple handlers?

Given this FastAPI app with two shutdown event handlers, what will be printed when the app shuts down?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.on_event("shutdown")
async def shutdown_event_1():
    print("Shutdown handler 1")

@app.on_event("shutdown")
async def shutdown_event_2():
    print("Shutdown handler 2")

A Both 'Shutdown handler 1' and 'Shutdown handler 2' are printed, order not guaranteed

B Only 'Shutdown handler 2' is printed

C No output is printed because shutdown handlers must be synchronous

D Only 'Shutdown handler 1' is printed

💡 Hint

Multiple shutdown handlers can be registered and all run on shutdown.

FastAPI runs all registered shutdown event handlers on app shutdown. The order is not guaranteed.

📝 Syntax

advanced

Identify the syntax error in this startup event handler

Which option shows the correct way to define a startup event handler in FastAPI without syntax errors?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.on_event("startup")
def startup_event():
    print("Starting")

A

@app.on_event("startup")
async def startup_event():
    print("Starting")

B

@app.on_event("startup")
def startup_event
    print("Starting")

C

@app.on_event("startup")
async startup_event():
    print("Starting")

D

@app.on_event("startup")
def startup_event():
print("Starting")

💡 Hint

Check function definition syntax and async keyword.

Option A correctly defines an async function with proper syntax. Others have syntax errors like missing colon or indentation.

❓ state_output

advanced

What is the value of the counter after app shutdown?

This FastAPI app increments a counter on startup and shutdown events. What is the final value of counter after the app starts and then shuts down?

FastAPI

from fastapi import FastAPI

app = FastAPI()
counter = 0

@app.on_event("startup")
async def startup_event():
    global counter
    counter += 1

@app.on_event("shutdown")
async def shutdown_event():
    global counter
    counter += 2

A 0

B 3

C 2

D 1

💡 Hint

Consider the order and increments during startup and shutdown.

Counter starts at 0, increments by 1 on startup, then by 2 on shutdown, total 3.

🔧 Debug

expert

Why does this shutdown event handler not run?

This FastAPI app has a shutdown event handler but it never prints its message when the app stops. Why?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.on_event("shutdown")
def shutdown_event():
    print("App is shutting down")

@app.get("/")
async def read_root():
    return {"msg": "Hello"}

A The shutdown event handler is missing the @app.shutdown decorator

B The shutdown event handler is synchronous but must be async to run

C The app must be run with a server that supports lifespan events for shutdown to trigger

D The shutdown event handler must be called manually inside a route

💡 Hint

Think about how FastAPI apps are run and how shutdown events are triggered.

Shutdown events only run if the server supports lifespan events, e.g., uvicorn with proper shutdown. Running app without server or with improper server prevents shutdown events.