Depends function basics in FastAPI - Mini Project: Build & Apply

Depends function basics

📖 Scenario: You are building a simple FastAPI web app that greets users. You want to use FastAPI's Depends function to inject a dependency that provides a greeting message.

🎯 Goal: Create a FastAPI app with a dependency function that returns a greeting message. Use Depends to inject this greeting into an endpoint that returns the message to the user.

📋 What You'll Learn

Create a dependency function called get_greeting that returns the string 'Hello, FastAPI!'.

Create a FastAPI app instance called app.

Create a GET endpoint at /greet that uses Depends(get_greeting) to receive the greeting message.

Return the greeting message as a JSON response with key message.

💡 Why This Matters

🌍 Real World

Using Depends in FastAPI helps organize code by separating concerns like authentication, database access, or configuration.

💼 Career

Understanding Depends is essential for building scalable and maintainable FastAPI applications in professional backend development.

1

Create the dependency function

Create a function called get_greeting that returns the string 'Hello, FastAPI!'.

FastAPI

# Your code here

Need a hint?

Define a simple function with no parameters that returns the greeting string.

2

Create the FastAPI app instance

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

FastAPI

def get_greeting():
    return 'Hello, FastAPI!'

# Your code here

Need a hint?

Use from fastapi import FastAPI and then app = FastAPI().

3

Create the GET endpoint using Depends

Import Depends from fastapi. Create a GET endpoint at /greet using @app.get("/greet"). Define a function greet that takes a parameter message which uses Depends(get_greeting).

FastAPI

from fastapi import FastAPI
from fastapi import Depends

def get_greeting():
    return 'Hello, FastAPI!'

app = FastAPI()

# Your code here

Need a hint?

Use @app.get("/greet") and a function with a parameter using Depends(get_greeting).

4

Return the greeting message as JSON

In the greet function, return a dictionary with key message and value message parameter to send JSON response.

FastAPI

from fastapi import FastAPI
from fastapi import Depends

def get_greeting():
    return 'Hello, FastAPI!'

app = FastAPI()

@app.get("/greet")
def greet(message: str = Depends(get_greeting)):
    # Your code here

Need a hint?

Return a dictionary with the greeting message to send JSON.