Status code control in FastAPI - Mini Project: Build & Apply

Status Code Control with FastAPI

📖 Scenario: You are building a simple web API using FastAPI. Your API will respond to client requests with different HTTP status codes depending on the situation.This is like a restaurant where the waiter tells you if your order is accepted, delayed, or not available by using different signals.

🎯 Goal: Create a FastAPI app with one endpoint that returns a JSON message and controls the HTTP status code explicitly.

📋 What You'll Learn

Create a FastAPI app instance named app

Define a GET endpoint at path /items/{item_id}

Use a variable item_id as a path parameter

Return a JSON response with a message and a status code

Return status code 200 if item_id is 1

Return status code 404 if item_id is not 1

💡 Why This Matters

🌍 Real World

APIs often need to tell clients if a request was successful or if something went wrong. Controlling status codes helps clients understand the result and handle it properly.

💼 Career

Knowing how to set HTTP status codes in FastAPI is essential for backend developers building reliable and clear APIs.

1

Create FastAPI app and define endpoint

Import FastAPI from fastapi and create an app instance called app. Then define a GET endpoint function called read_item with a path parameter item_id of type int at path /items/{item_id}.

FastAPI

from fastapi import FastAPI

# Create FastAPI app instance
# Define GET endpoint /items/{item_id} with function read_item(item_id: int)
# Your code here

Need a hint?

Start by importing FastAPI and creating an app instance. Then use the @app.get decorator with the path /items/{item_id}. Define an async function read_item that takes item_id as an integer parameter.

2

Add a status code variable

Inside the read_item function, create a variable called status_code and set it to 200.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    # Create status_code variable and set to 200
    # Your code here

Need a hint?

Inside the function, write status_code = 200 to start with a default success code.

3

Change status code for missing item

Add an if statement inside read_item to check if item_id is not equal to 1. If so, set status_code to 404.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    status_code = 200
    # If item_id is not 1, set status_code to 404
    # Your code here

Need a hint?

Use an if statement to check if item_id is not 1, then assign status_code = 404.

4

Return JSON response with status code

Set a message to "Item found" if status_code == 200 else "Item not found". Return JSONResponse(content={"message": message}, status_code=status_code).

FastAPI

from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    status_code = 200
    if item_id != 1:
        status_code = 404
    # Return JSONResponse with message and status_code
    # Your code here

Need a hint?

Import JSONResponse from fastapi.responses. Use a conditional expression to set the message. Return JSONResponse with content as a dictionary and status_code as the HTTP status.