Logging errors in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output when logging an error with FastAPI's logger?

Given this FastAPI code snippet, what will be printed in the console when a GET request to '/' triggers an error log?

import logging
from fastapi import FastAPI

app = FastAPI()
logger = logging.getLogger("uvicorn.error")

@app.get("/")
def read_root():
    try:
        1 / 0
    except ZeroDivisionError as e:
        logger.error(f"Error occurred: {e}")
        return {"message": "Error logged"}

FastAPI

import logging
from fastapi import FastAPI

app = FastAPI()
logger = logging.getLogger("uvicorn.error")

@app.get("/")
def read_root():
    try:
        1 / 0
    except ZeroDivisionError as e:
        logger.error(f"Error occurred: {e}")
        return {"message": "Error logged"}

A ERROR: Error occurred: division by zero

B WARNING: Error occurred: division by zero

C INFO: Error occurred: division by zero

D No output is printed because logging is disabled by default

💡 Hint

Think about the logging level used in the logger.error call.

The logger.error method logs messages with ERROR level. By default, Uvicorn's error logger prints ERROR level messages to the console.

❓ Configuration

intermediate

How to configure FastAPI logging to write errors to a file?

Which logging configuration snippet correctly sets up FastAPI to write error logs to a file named 'error.log' with level ERROR?

A logging.basicConfig(filename='error.log', level='ERROR', format='%(levelname)s:%(message)s')

B logging.basicConfig(filename='error.log', level=logging.DEBUG, format='%(message)s')

C logging.basicConfig(filename='error.log', level=logging.ERROR, format='%(levelname)s:%(message)s')

D logging.basicConfig(file='error.log', level=logging.ERROR, format='%(levelname)s:%(message)s')

💡 Hint

Check the parameter names and logging level types.

The filename parameter sets the log file, level expects a logging level constant, and format defines the log message format.

❓ Troubleshoot

advanced

Why are error logs not appearing in FastAPI when using logger.error?

You added logger.error("An error happened") in your FastAPI app, but no error messages appear in the console or log files. What is the most likely cause?

A The error message is printed only if an exception is raised, not manually logged

B The logger.error method does not print messages, only logger.warning does

C FastAPI disables logging by default and requires manual enabling

D The logging level is set higher than ERROR, so error messages are ignored

💡 Hint

Check the logging level configuration in your app or server.

If the logging level is set to CRITICAL, for example, ERROR messages will not show. The logger.error method does print messages if the level allows.

🔀 Workflow

advanced

What is the correct workflow to capture and log exceptions globally in FastAPI?

Which approach correctly logs all unhandled exceptions globally in a FastAPI app?

A Use a custom exception handler with @app.exception_handler(Exception) that logs the error and returns a response

B Set logging.basicConfig(level=logging.ERROR) and rely on FastAPI to log automatically

C Wrap every route handler in try-except blocks and log errors inside each

D Use middleware to catch exceptions but do not log them, only return error responses

💡 Hint

Think about a centralized way to handle all exceptions.

A global exception handler catches all exceptions, logs them, and returns a response. Wrapping every route is tedious and error-prone.

✅ Best Practice

expert

Which is the best practice for logging sensitive error details in FastAPI production apps?

In a production FastAPI app, how should you handle logging of sensitive error details to avoid security risks?

A Always log full error details and stack traces to the client response for easier debugging

B Log detailed error stack traces only to secure internal log files, and return generic error messages to clients

C Disable all error logging in production to prevent any sensitive data exposure

D Log error details only in client responses and not in any log files

💡 Hint

Consider security and privacy best practices for error information.

Detailed error logs should be kept internally for developers, while clients receive safe, generic messages to avoid exposing sensitive info.