A very basic REST API - Python Snacks

app.py

# To run this application, you'll need to install 3 packages:
#   pip install pandas
#   pip install fastapi
#   pip install uvicorn
# In the command line to run the application, type `uvicorn app:app --reload`

# Note: if using uv:
#   uv bare --init
#   uv add pandas fastapi uvicorn
#   uv run uvicorn app:app --reload
from fastapi import FastAPI, HTTPException
import pandas as pd
from pathlib import Path
import uvicorn

CSV_FILE = Path("items.csv")
app = FastAPI()


def load_df():
    return pd.read_csv(CSV_FILE)


def save_df(df):
    df.to_csv(CSV_FILE, index=False)


@app.get("/items")
def get_items():
    df = load_df()
    return df.to_dict(orient="records")


@app.get("/items/{item_id}")
def get_item(item_id: int):
    df = load_df()
    match = df[df["id"] == item_id]

    if match.empty:
        raise HTTPException(404, "Item not found")

    return match.iloc[0].to_dict()


@app.post("/items")
def create_item(item: dict):
    df = load_df()

    if df[df["id"] == item.get("id")].shape[0] > 0:
        raise HTTPException(400, "ID already exists")

    df = pd.concat([df, pd.DataFrame([item])], ignore_index=True)
    save_df(df)

    return item


@app.put("/items/{item_id}")
def replace_item(item_id: int, item: dict):
    df = load_df()

    if item_id not in df["id"].values:
        raise HTTPException(404, "Item not found")

    # Get row index to update
    row_index = df.index[df["id"] == item_id][0]

    # Replace the entire row explicitly
    df.loc[row_index, "id"] = item["id"]
    df.loc[row_index, "name"] = item["name"]
    df.loc[row_index, "description"] = item["description"]

    save_df(df)
    return item


@app.patch("/items/{item_id}")
def update_item(item_id: int, updates: dict):
    df = load_df()

    if item_id not in df["id"].values:
        raise HTTPException(404, "Item not found")

    row_index = df.index[df["id"] == item_id][0]

    for key, value in updates.items():
        df.at[row_index, key] = value

    save_df(df)

    return df.iloc[row_index].to_dict()


@app.delete("/items/{item_id}")
def delete_item(item_id: int):
    df = load_df()

    if item_id not in df["id"].values:
        raise HTTPException(404, "Item not found")

    df = df[df["id"] != item_id]
    save_df(df)

    return {"status": "deleted"}

items.csv

make_request.py

# This code is the driver code to get data from your server without
#   ever having to worry about HOW to access the database.

# You'll need to install requests:
#   pip install requests

# If using uv:
#   uv add requests

import requests

BASE_URL = "http://127.0.0.1:8000"


# Fetch every item from the API
def get_all_items():
    resp = requests.get(f"{BASE_URL}/items")
    return resp.json()


# Fetch a single item by its ID
def get_item(item_id: int):
    resp = requests.get(f"{BASE_URL}/items/{item_id}")
    return resp.json()


# Add a brand new item to the CSV via the API
def create_item(item: dict):
    resp = requests.post(f"{BASE_URL}/items", json=item)
    return resp.json()


# Replace an existing item completely (all fields)
def replace_item(item_id: int, item: dict):
    resp = requests.put(f"{BASE_URL}/items/{item_id}", json=item)
    return resp.json()


# Update only specific fields of an item
def update_item(item_id: int, updates: dict):
    resp = requests.patch(f"{BASE_URL}/items/{item_id}", json=updates)
    return resp.json()


# Delete an item from the CSV by ID
def delete_item(item_id: int):
    resp = requests.delete(f"{BASE_URL}/items/{item_id}")
    return resp.json()


if __name__ == "__main__":
    print("\n--- Initial GET (all items) ---")
    print(get_all_items())

    print("\n--- POST: Create a new item ---")
    new_item = {"id": 10, "name": "Pear", "description": "Green fruit"}
    print(create_item(new_item))

    print("\n--- GET: Fetch the new item ---")
    print(get_item(10))

    print("\n--- PUT: Replace the item entirely ---")
    replaced_item = {"id": 10, "name": "Pear", "description": "Fully updated pear"}
    print(replace_item(10, replaced_item))

    print("\n--- PATCH: Update only one field ---")
    print(update_item(10, {"description": "Pear with new description"}))

    print("\n--- DELETE: Remove the item ---")
    print(delete_item(10))

    print("\n--- Final GET (all items) ---")
    print(get_all_items())