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.

Practice

1. What is the main purpose of using logger.error() with exc_info=True in a FastAPI application?

easy

A. To send an email notification when an error occurs

B. To log detailed error information including the stack trace

C. To automatically restart the FastAPI server on errors

D. To disable error logging temporarily

Solution

1. Step 1: Understand the role of logger.error()

   This method logs error messages in the application logs.

2. Step 2: Explain the effect of exc_info=True

   This argument adds the full exception traceback to the log, helping with debugging.

3. Final Answer:

   To log detailed error information including the stack trace -> Option B

4. Quick Check:

   Logging errors with traceback = A [OK]

Hint: Remember: exc_info=True shows full error details [OK]

Common Mistakes:

• Thinking logger.error() restarts the server
• Confusing error logging with notifications
• Assuming exc_info=True disables logging

2. Which of the following is the correct way to log an error with exception info in FastAPI using Python's logging module?

easy

A. logger.error("Error occurred")

B. logger.error(exc_info=True)

C. logger.error("Error occurred", exception=True)

D. logger.error("Error occurred", exc_info=True)

Solution

1. Step 1: Review the logging.error() method signature

   The method accepts a message string and optional keyword arguments like exc_info.

2. Step 2: Identify the correct usage to include exception info

   Using exc_info=True includes the traceback in the log output.

3. Final Answer:

   logger.error("Error occurred", exc_info=True) -> Option D

4. Quick Check:

   Use exc_info=True to log exceptions [OK]

Hint: Use exc_info=True inside logger.error() for full error trace [OK]

Common Mistakes:

• Omitting exc_info argument
• Passing exc_info as a positional argument
• Using non-existent argument 'exception=True'

3. Given this FastAPI error logging code snippet, what will be the output in the logs?

try:
    1 / 0
except Exception as e:
    logger.error("Division failed", exc_info=True)

medium

A. Logs only the message 'Division failed' without error details

B. Raises a ZeroDivisionError and stops the program

C. Logs the message 'Division failed' with a ZeroDivisionError traceback

D. Logs nothing because exception is caught

Solution

1. Step 1: Analyze the try-except block

   The code attempts division by zero, which raises ZeroDivisionError caught by except.

2. Step 2: Understand logger.error with exc_info=True

   It logs the message plus the full traceback of the caught exception.

3. Final Answer:

   Logs the message 'Division failed' with a ZeroDivisionError traceback -> Option C

4. Quick Check:

   exc_info=True logs error trace [OK]

Hint: exc_info=True logs full error trace, not just message [OK]

Common Mistakes:

• Thinking the error stops the program
• Assuming no traceback is logged
• Believing the log is empty on exception

4. You wrote this FastAPI error logging code but no error details appear in logs:

try:
    open('missing_file.txt')
except Exception:
    logger.error("File open failed")

What is the main fix to log the error details?

medium

A. Add exc_info=True to logger.error call

B. Change except Exception to except FileNotFoundError

C. Use logger.info instead of logger.error

D. Remove the try-except block

Solution

1. Step 1: Identify missing error detail logging

   The current logger.error call logs only the message without exception info.

2. Step 2: Add exc_info=True to include traceback

   Passing exc_info=True logs the full exception details automatically.

3. Final Answer:

   Add exc_info=True to logger.error call -> Option A

4. Quick Check:

   Include exc_info=True to log error details [OK]

Hint: Always add exc_info=True to log exceptions fully [OK]

Common Mistakes:

• Changing exception type without logging fix
• Using logger.info which is lower severity
• Removing try-except causing crashes

5. You want to log errors in a FastAPI app only when an exception occurs, including the traceback, but avoid logging if no error happens. Which code snippet correctly implements this?

hard

A. try:
risky_operation()
except Exception as e:
logger.error("Operation failed", exc_info=True)

B. logger.error("Operation failed", exc_info=True)
risky_operation()

C. try:
risky_operation()
except Exception:
logger.error("Operation failed")

D. try:
risky_operation()
except Exception as e:
logger.error("Operation failed")

Solution

1. Step 1: Ensure error logging happens only on exceptions

   Logging must be inside except block to avoid logging when no error occurs.

2. Step 2: Include exc_info=True to log traceback

   Passing exc_info=True ensures full error details are logged.

3. Final Answer:

   try: risky_operation() except Exception as e: logger.error("Operation failed", exc_info=True) -> Option A

4. Quick Check:

   Log errors with traceback only on exceptions [OK]

Hint: Log errors inside except with exc_info=True [OK]

Common Mistakes:

• Logging errors outside try-except block
• Omitting exc_info=True losing traceback
• Logging without exception object