Logging configuration in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of logging configuration with custom format

Given this FastAPI logging setup, what will be the output when a GET request is made to '/'?

FastAPI

import logging
from fastapi import FastAPI

app = FastAPI()

logging.basicConfig(level=logging.INFO, format='%(levelname)s:%(message)s')
logger = logging.getLogger(__name__)

@app.get('/')
async def root():
    logger.info('Root endpoint accessed')
    return {'message': 'Hello World'}

A INFO:root endpoint accessed

B INFO:Root endpoint accessed

C root endpoint accessed

D Logging not configured

💡 Hint

Check the logging format string and case sensitivity.

The logging format specifies level name in uppercase followed by a colon and the message. The message is exactly 'Root endpoint accessed' with capital R.

❓ Configuration

intermediate

Correct YAML logging config for rotating file handler

Which YAML snippet correctly configures a rotating file handler for FastAPI logs with max 5 files and 1MB each?

A

version: 1
handlers:
  file:
    class: logging.handlers.RotatingFileHandler
    filename: app.log
    maxBytes: 1048576
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

B

version: 1
handlers:
  file:
    class: logging.FileHandler
    filename: app.log
    maxBytes: 1048576
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

C

version: 1
handlers:
  file:
    class: logging.handlers.TimedRotatingFileHandler
    filename: app.log
    when: 'midnight'
    backupCount: 5
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

D

version: 1
handlers:
  file:
    class: logging.handlers.RotatingFileHandler
    filename: app.log
    maxBytes: 512000
    backupCount: 10
    level: INFO
loggers:
  uvicorn:
    handlers: [file]
    level: INFO

💡 Hint

RotatingFileHandler requires maxBytes and backupCount for size-based rotation.

Option A correctly uses RotatingFileHandler with maxBytes 1MB (1048576 bytes) and backupCount 5. Others either use wrong handler or wrong sizes.

❓ Troubleshoot

advanced

Why are logs missing in production with this FastAPI setup?

You configured logging in FastAPI with this code but see no logs in production. What is the most likely cause? import logging logging.basicConfig(level=logging.DEBUG) logger = logging.getLogger('uvicorn.error') logger.info('App started')

A Missing call to logger.setLevel() to enable logging

B Logging level DEBUG is too low to show info messages

C Logger name 'uvicorn.error' does not exist, so no logs are captured

D Uvicorn overrides logging config; basicConfig is ignored when running with uvicorn server

💡 Hint

Consider how uvicorn manages logging internally.

Uvicorn configures logging itself when started, so calling basicConfig in app code is ignored. Logs must be configured via uvicorn or external config.

🔀 Workflow

advanced

Order steps to enable JSON logging in FastAPI with uvicorn

Arrange these steps in the correct order to enable JSON formatted logs in a FastAPI app running with uvicorn.

A 1,2,3,4

B 1,3,2,4

C 2,1,3,4

D 3,1,2,4

💡 Hint

Think about installing dependencies before using them.

First install the package, then create the formatter, configure uvicorn to use it, and finally run uvicorn with that config.

✅ Best Practice

expert

Which logging practice improves FastAPI app observability in production?

Select the best practice that improves observability and troubleshooting in a production FastAPI app.

A Log only error messages to reduce log volume

B Log all debug messages to a single file without rotation

C Use structured logging with JSON format including request IDs and timestamps

D Disable logging to improve performance

💡 Hint

Think about how logs help in tracing and analyzing issues.

Structured JSON logs with request IDs and timestamps help correlate events and improve observability. Other options reduce usefulness or cause issues.

Practice

1. What is the main purpose of configuring logging in a FastAPI application?

easy

A. To track app activity and errors for easier debugging

B. To speed up the app's response time

C. To automatically update the app's dependencies

D. To create user interface themes

Solution

1. Step 1: Understand logging purpose

   Logging records events and errors during app execution.

2. Step 2: Connect to debugging

   Tracking these events helps developers find and fix issues.

3. Final Answer:

   To track app activity and errors for easier debugging -> Option A

4. Quick Check:

   Logging = Track activity/errors [OK]

Hint: Logging is for tracking events and errors [OK]

Common Mistakes:

• Confusing logging with performance optimization
• Thinking logging updates app code automatically
• Mixing logging with UI design

2. Which of the following is the correct way to set up basic logging in a FastAPI app using Python's logging module?

easy

A. log.config(level=logging.DEBUG)

B. logging.setup(level='DEBUG')

C. logging.basicConfig(level=logging.DEBUG)

D. logging.start(level=logging.DEBUG)

Solution

1. Step 1: Recall Python logging setup

   The standard method is logging.basicConfig() to configure logging.

2. Step 2: Check syntax correctness

   logging.basicConfig(level=logging.DEBUG) correctly sets the log level.

3. Final Answer:

   logging.basicConfig(level=logging.DEBUG) -> Option C

4. Quick Check:

   Use basicConfig for logging setup [OK]

Hint: Use logging.basicConfig() to configure logging [OK]

Common Mistakes:

• Using non-existent logging.setup() method
• Misspelling logging as log
• Using start() instead of basicConfig()

3. Given this FastAPI logging setup code:

import logging
logging.basicConfig(level=logging.WARNING)
logging.debug('Debug message')
logging.warning('Warning message')

What will be printed to the console?

medium

A. Warning message

B. Debug message

C. Debug message\nWarning message

D. No output

Solution

1. Step 1: Understand logging levels

   Level WARNING means only WARNING and above are shown, DEBUG is lower level.

2. Step 2: Check which messages print

   DEBUG message is ignored, WARNING message is printed.

3. Final Answer:

   Warning message -> Option A

4. Quick Check:

   Level WARNING shows warnings only [OK]

Hint: Only messages at or above set level print [OK]

Common Mistakes:

• Expecting DEBUG messages to print at WARNING level
• Thinking all messages print regardless of level
• Confusing logging levels order

4. You wrote this code to configure logging:

import logging
logging.basicConfig(level='DEBUG')
logging.info('Info message')

But no output appears. What is the likely problem?

medium

A. You need to import sys module first

B. The level argument should be logging.DEBUG, not a string

C. basicConfig() must be called after logging.info()

D. logging.info() does not print messages

Solution

1. Step 1: Check logging level argument type

   logging.basicConfig expects level as a constant like logging.DEBUG, not a string.

2. Step 2: Understand effect of wrong level

   Passing 'DEBUG' string is ignored, default level WARNING applies, so info messages don't show.

3. Final Answer:

   The level argument should be logging.DEBUG, not a string -> Option B

4. Quick Check:

   Level must be logging.DEBUG constant [OK]

Hint: Use logging.DEBUG constant, not string 'DEBUG' [OK]

Common Mistakes:

• Passing level as string instead of constant
• Calling basicConfig after logging calls
• Assuming info messages never print

5. You want to log messages to a file named app.log with level INFO and include timestamps. Which is the correct logging configuration code?

hard

A. logging.basicConfig(file='app.log', level='INFO', format='%(time)s - %(msg)s')

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

C. logging.setup(filename='app.log', level=logging.INFO, format='%(asctime)s - %(message)s')

D. logging.basicConfig(filename='app.log', level=logging.INFO, format='%(asctime)s - %(message)s')

Solution

1. Step 1: Check correct parameter names

   logging.basicConfig uses filename, level, and format parameters correctly.

2. Step 2: Verify format string and level

   Format '%(asctime)s - %(message)s' adds timestamp; level INFO matches requirement.

3. Final Answer:

   logging.basicConfig(filename='app.log', level=logging.INFO, format='%(asctime)s - %(message)s') -> Option D

4. Quick Check:

   Use filename, level=logging.INFO, correct format [OK]

Hint: Use filename and format with %(asctime)s for timestamps [OK]

Common Mistakes:

• Using wrong parameter names like file instead of filename
• Passing level as string instead of constant
• Incorrect format placeholders