FastAPI: apps and routes

FastAPI maps URL paths and HTTP methods to Python functions. JSON dict return values become JSON responses.

Minimal app

A typical minimal FastAPI module looks like this:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def root():
    return {"hello": "world"}

@app.get("/ping")
def ping():
    return {"message": "pong"}

@app.post("/alive")
def alive():
    return {"message": "you're alive!"}

• @app.get("/path") registers a GET route.
• @app.post(...) registers POST.
• Return a dict → JSON object; return a list → JSON array.

Note

Typos in keys (e.g. mesage vs message) become typos in JSON—clients and tests should match the exact spelling you intend.

Path vs query parameters (preview)

@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}

FastAPI parses and validates types for you.

Implement

1. Complete Virtual environments and packages so FastAPI is installed in your venv.
2. Create app.py (or the filename your template uses) with app = FastAPI().
3. Add GET / returning any small JSON dict.
4. Add GET /ping returning {"message": "pong"} (your capstone route—keep it working from here on).
5. Commit and push (application code only—not personal test files).