Why file operations are common in FastAPI - See It in Action

Why File Operations Are Common in FastAPI

📖 Scenario: You are building a simple FastAPI app that handles user-uploaded files. This is common in many real-world apps like photo sharing, document storage, or profile picture uploads.

🎯 Goal: Learn why file operations are common in FastAPI by creating a small app that accepts a file upload and saves it on the server.

📋 What You'll Learn

Create a FastAPI app instance called app

Create an endpoint /uploadfile/ that accepts a file upload using UploadFile

Save the uploaded file to disk with the exact filename uploaded_file.txt

Return a JSON response confirming the file was saved

💡 Why This Matters

🌍 Real World

Many web apps let users upload files like photos, resumes, or reports. FastAPI makes it easy to accept and save these files securely.

💼 Career

Backend developers often build APIs that handle file uploads and storage. Knowing how to do file operations in FastAPI is a valuable skill.

1

DATA SETUP: Import FastAPI and create app instance

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

FastAPI

# Import FastAPI and create app instance
# Your code here

Hint

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

2

CONFIGURATION: Import UploadFile and File for file uploads

Import UploadFile and File from fastapi to handle file uploads.

FastAPI

from fastapi import FastAPI
# Import UploadFile and File below
# Your code here

Hint

Use from fastapi import UploadFile, File along with FastAPI.

3

CORE LOGIC: Create POST endpoint to accept and save uploaded file

Create a POST endpoint /uploadfile/ using @app.post. Define an async function upload_file that accepts a parameter file of type UploadFile using File(...). Inside the function, open a file named uploaded_file.txt in write-binary mode and write the contents of the uploaded file to it using await file.read(). Return a dictionary with key filename and value uploaded_file.txt.

FastAPI

from fastapi import FastAPI, UploadFile, File

app = FastAPI()

# Create POST endpoint /uploadfile/ to accept and save uploaded file
# Your code here

Hint

Use @app.post("/uploadfile/") and an async function with file: UploadFile = File(...). Read file content with await file.read() and write it to uploaded_file.txt.

4

COMPLETION: Add a root GET endpoint with a welcome message

Add a GET endpoint / using @app.get that returns a dictionary with key message and value "Welcome to the file upload app!".

FastAPI

from fastapi import FastAPI, UploadFile, File

app = FastAPI()

@app.post("/uploadfile/")
async def upload_file(file: UploadFile = File(...)):
    contents = await file.read()
    with open("uploaded_file.txt", "wb") as f:
        f.write(contents)
    return {"filename": "uploaded_file.txt"}

# Add GET endpoint / with welcome message
# Your code here

Hint

Use @app.get("/") and a function read_root that returns the welcome message dictionary.