Path parameters in FastAPI - Mini Project: Build & Apply

Using Path Parameters in FastAPI

📖 Scenario: You are building a simple web API for a bookstore. You want to create endpoints that can receive book IDs directly in the URL path to fetch details about specific books.

🎯 Goal: Build a FastAPI app that uses path parameters to get book details by their ID.

📋 What You'll Learn

Create a FastAPI app instance

Define a path parameter called book_id in the route

Return a dictionary with the book_id in the response

💡 Why This Matters

🌍 Real World

APIs often need to get specific resources by ID or name directly from the URL path. This project shows how to do that with FastAPI.

💼 Career

Understanding path parameters is essential for backend developers building RESTful APIs with FastAPI or similar frameworks.

1

Create a FastAPI app instance

Import FastAPI from fastapi and create an app instance called app.

FastAPI

from fastapi import FastAPI

# Create the FastAPI app instance called app
# Your code here

Need a hint?

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

2

Define a path parameter in the route

Create a GET route at /books/{book_id} using @app.get. Define a function called read_book that takes book_id as an integer parameter.

FastAPI

from fastapi import FastAPI

app = FastAPI()

# Create a GET route at /books/{book_id} with a function read_book(book_id: int)
# Your code here

Need a hint?

Use @app.get("/books/{book_id}") and define read_book(book_id: int).

3

Return the book ID in the response

Inside the read_book function, return a dictionary with the key book_id and the value from the book_id parameter.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/books/{book_id}")
def read_book(book_id: int):
    # Return a dictionary with book_id
    # Your code here

Need a hint?

Return {"book_id": book_id} to send the book ID back.

4

Add type hint and run the app

Make sure the book_id parameter in read_book has the type hint int. This helps FastAPI convert the path parameter to an integer automatically.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/books/{book_id}")
def read_book(book_id: int):
    return {"book_id": book_id}

# Ensure book_id has type int for automatic conversion
# Your code here

Need a hint?

Type hint book_id: int is required for FastAPI to parse the path parameter as an integer.