Logging errors in FastAPI - Mini Project: Build & Apply

Logging errors in FastAPI

📖 Scenario: You are building a simple web API using FastAPI. You want to keep track of errors that happen when users call your API. Logging errors helps you find and fix problems quickly.

🎯 Goal: Create a FastAPI app that logs error messages when an exception happens in an endpoint.

📋 What You'll Learn

Create a FastAPI app instance called app

Set up a logger named logger using Python's logging module

Add a configuration to log error messages to the console

Create an endpoint /divide that divides two query parameters a and b

Catch division errors and log the error message using logger.error

Return a JSON response with the error message when division by zero occurs

💡 Why This Matters

🌍 Real World

Logging errors in web APIs helps developers quickly find and fix bugs, improving app reliability.

💼 Career

Understanding error logging is essential for backend developers and DevOps engineers to maintain healthy production systems.

1

Create FastAPI app and import logging

Import FastAPI from fastapi and logging. Create a FastAPI app instance called app.

FastAPI

from fastapi import FastAPI
import logging

# Your code here

Need a hint?

Use app = FastAPI() to create the app instance.

2

Set up logger to log errors to console

Create a logger named logger using logging.getLogger(__name__). Set the logger level to logging.ERROR. Add a StreamHandler to output logs to the console.

FastAPI

from fastapi import FastAPI
import logging

app = FastAPI()

# Your code here

Need a hint?

Use logging.getLogger(__name__) to create the logger and logger.setLevel(logging.ERROR) to set the level.

3

Create /divide endpoint with error logging

Create a GET endpoint /divide that accepts query parameters a and b as floats. Inside the function, try to divide a by b. If a ZeroDivisionError occurs, log the error message using logger.error and return a JSON response with key error and a message "Cannot divide by zero".

FastAPI

from fastapi import FastAPI
import logging

app = FastAPI()

logger = logging.getLogger(__name__)
logger.setLevel(logging.ERROR)
console_handler = logging.StreamHandler()
logger.addHandler(console_handler)

# Your code here

Need a hint?

Use try and except ZeroDivisionError as e to catch the error and log it.

4

Print a test log message

Add a line to log an error message "Test error log" using logger.error.

FastAPI

from fastapi import FastAPI
import logging
from fastapi import Query
from fastapi.responses import JSONResponse

app = FastAPI()

logger = logging.getLogger(__name__)
logger.setLevel(logging.ERROR)
console_handler = logging.StreamHandler()
logger.addHandler(console_handler)

@app.get('/divide')
async def divide(a: float = Query(...), b: float = Query(...)):
    try:
        result = a / b
        return {"result": result}
    except ZeroDivisionError as e:
        logger.error(f"Division error: {e}")
        return JSONResponse(status_code=400, content={"error": "Cannot divide by zero"})

# Your code here

Need a hint?

Use logger.error("Test error log") to print the test message.