Logging configuration in FastAPI - Mini Project: Build & Apply

Logging configuration

📖 Scenario: You are building a simple FastAPI application. To keep track of what happens in your app, you want to set up logging. Logging helps you see messages about your app's actions, errors, and important events.

🎯 Goal: Set up basic logging in a FastAPI app that writes messages to the console with a specific format.

📋 What You'll Learn

Create a logger named app_logger

Set the logging level to INFO

Configure the logger to output messages with the format: %(levelname)s:%(message)s

Log an INFO message saying App started

💡 Why This Matters

🌍 Real World

Logging is essential in real applications to monitor what the app is doing and to help find problems quickly.

💼 Career

Understanding logging setup is a key skill for DevOps and backend developers to maintain and troubleshoot applications.

1

Create a FastAPI app and import logging

Write code to import the FastAPI class from fastapi and the logging module. Then create a FastAPI app instance called app.

FastAPI

from fastapi import FastAPI
import logging

# Your code here

Hint

Use from fastapi import FastAPI and app = FastAPI() to create the app.

2

Create a logger named app_logger and set level to INFO

Create a logger called app_logger using logging.getLogger with the name app_logger. Set its logging level to logging.INFO.

FastAPI

from fastapi import FastAPI
import logging

app = FastAPI()

# Your code here

Hint

Use logging.getLogger('app_logger') and setLevel(logging.INFO).

3

Add a console handler with a simple message format

Create a StreamHandler for app_logger to output logs to the console. Set its format to %(levelname)s:%(message)s using a Formatter. Add this handler to app_logger.

FastAPI

from fastapi import FastAPI
import logging

app = FastAPI()

app_logger = logging.getLogger('app_logger')
app_logger.setLevel(logging.INFO)

# Your code here

Hint

Create a StreamHandler, set its formatter, then add it to app_logger.

4

Log an INFO message 'App started'

Use app_logger.info to log the message 'App started'.

FastAPI

from fastapi import FastAPI
import logging

app = FastAPI()

app_logger = logging.getLogger('app_logger')
app_logger.setLevel(logging.INFO)

console_handler = logging.StreamHandler()
formatter = logging.Formatter('%(levelname)s:%(message)s')
console_handler.setFormatter(formatter)
app_logger.addHandler(console_handler)

# Your code here

Hint

Call app_logger.info('App started') to log the message.

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