Logging errors in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of logging errors in FastAPI?

Logging errors helps track problems in your application so you can fix them quickly. It records what went wrong and when, like keeping a diary of mistakes.

beginner

Which Python module is commonly used for logging errors in FastAPI?

The built-in logging module is used to record error messages and other information in FastAPI applications.

beginner

How do you log an error message in FastAPI using the logging module?

You first import logging, then create a logger, and use <code>logger.error('Your error message')</code> to log errors.

intermediate

Why is it helpful to include exception details in error logs?

Including exception details shows exactly what went wrong, making it easier to understand and fix the problem.

intermediate

What is a simple way to configure logging format in FastAPI?

Use logging.basicConfig() to set the format, like time, level, and message, so logs are clear and easy to read.

Which Python module is used to log errors in FastAPI?

A logging

B os

C sys

D json

The logging module is the standard way to log errors and messages in Python and FastAPI.

What method logs an error message using a logger?

A logger.info()

B logger.debug()

C logger.warning()

D logger.error()

logger.error() is used to log error messages.

Why include exception details in error logs?

A To understand the cause of errors

B To confuse developers

C To slow down the app

D To make logs longer

Exception details help understand what caused the error, making fixing easier.

Which function sets the logging format simply?

A logging.setLevel()

B logging.basicConfig()

C logging.getLogger()

D logging.error()

logging.basicConfig() configures the logging format and level.

What is a good practice when logging errors in FastAPI?

A Ignore exceptions

B Log only success messages

C Log error messages with details

D Delete logs regularly

Logging error messages with details helps track and fix issues effectively.

Explain how to set up basic error logging in a FastAPI application.

Think about importing the logging module and how to write error messages.

Why is logging errors important in FastAPI, and what details should you include?

Consider how logs help you fix issues later.

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