Module 3 Exercises: Building the Skeleton

You've learned how to move from a single script to a production-grade architecture. These exercises will test your ability to organize and secure a project.

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Exercise 1: The Router Inclusion

You are building a Social Media API. You have created a file called api/v1/posts.py with the following content:

from fastapi import APIRouter

router = APIRouter()

@router.get("/feed")
def get_feed():
    return {"posts": []}

Write the code needed in your main.py to include this router so that the feed is accessible at the URL /api/v1/posts/feed.

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Exercise 2: The .gitignore Audit

Which of the following files should NEVER be committed to a public Git repository? (Select all that apply)

1. main.py
2. .env
3. requirements.txt
4. .venv/
5. pyproject.toml
6. secrets.json

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Exercise 3: Pydantic Settings Design

Design a Settings class using pydantic-settings for an Email Marketing App. The class should handle three variables:

• SERVICE_NAME (String, default: "MailFast")
• MAX_EMAILS_PER_DAY (Integer, no default)
• USE_SANDBOX_MODE (Boolean, default: True)

How would your .env file look if you wanted to set the max emails to 5000 and turn off sandbox mode?

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Self-Correction / Discussion

Exercise 1 Answer:

from fastapi import FastAPI
from app.api.v1 import posts

app = FastAPI()

app.include_router(
    posts.router, 
    prefix="/api/v1/posts", 
    tags=["posts"]
)

Exercise 2 Answer:

2, 4, and 6.

• .env contains secrets.
• .venv/ is environment-specific and massive.
• secrets.json contains... well, secrets! Note: requirements.txt and pyproject.toml SHOULD be committed so others can recreate your environment.

Exercise 3 Answer:

from pydantic_settings import BaseSettings

class Settings(BaseSettings):
    service_name: str = "MailFast"
    max_emails_per_day: int
    use_sandbox_mode: bool = True

settings = Settings()

.env file:

MAX_EMAILS_PER_DAY=5000
USE_SANDBOX_MODE=False

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Summary of Module 3

You now know how to build the "House" for your code.

• Structure: You can modularize with APIRouter.
• Isolation: You can protect your environment with Venv/Poetry.
• Security: You can manage secrets via Environment Variables.

In Module 4: Routing and Request Handling, we will dive back into the code to master how FastAPI processes incoming path and query parameters.