Form Data & File Uploads
Handle traditional HTML form data and implement file uploads using FastAPI's built-in capabilities.
Form Data & File Uploads is a free FastAPI Backend Development Bootcamp lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the FastAPI Backend Development Bootcamp learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Form Data Basics
When you fill out a web form (like a login or registration page) and click "submit," the data you entered is often sent as form data.
This is a traditional way for browsers to send information to a server, different from sending JSON in a request body.
Form data can be sent in two main ways:
application/x-www-form-urlencoded: For simple key-value pairs.multipart/form-data: Used when files are involved, or for larger, more complex data.
FastAPI's Form Dependency
FastAPI makes handling form data easy using the Form dependency from fastapi.
It works similarly to Query or Path parameters, but it tells FastAPI to expect the data in the request body as form fields.
You import it like this: from fastapi import FastAPI, Form.
Basic Form Endpoint Example
Let's create an endpoint that accepts a username and password as form data. Notice how username and password are explicitly marked with Form(...).
This tells FastAPI to parse them from the form body, not as JSON or query parameters.
from fastapi import FastAPI, Form
import uvicorn
app = FastAPI()
@app.post("/login/")
async def login(username: str = Form(...), password: str = Form(...)):
return {"username": username, "message": "Login successful!"}
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)Interacting with Form Data
You can test this endpoint using tools like curl or by creating a simple HTML form. The -d flag in curl sends form data.
Make sure your FastAPI application from the previous scene is running!
curl -X POST "http://127.0.0.1:8000/login/" \
-H "Content-Type: application/x-www-form-urlencoded" \
-d "username=coddy&password=secret"File Uploads Explained
Uploading files (like images, documents, or videos) is a common web task. This type of data is sent using multipart/form-data encoding.
FastAPI provides special tools to handle these uploads efficiently, allowing you to access file contents and metadata.
FastAPI's UploadFile
For file uploads, FastAPI uses the UploadFile class (from fastapi) along with the File dependency.
When you declare a parameter with File(...) and type-hint it as UploadFile, FastAPI handles the file stream.
filename: The name of the uploaded file.content_type: The file's MIME type (e.g.,image/jpeg).file: A SpooledTemporaryFile object, allowing you to read its contents.
from fastapi import FastAPI, File, UploadFile
import uvicorn
app = FastAPI()
@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile = File(...)):
return {"filename": file.filename, "content_type": file.content_type}
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)Saving One Uploaded File
After receiving an UploadFile, you can read its content and save it to a local disk or cloud storage. Here's how to save it locally.
Remember to handle potential errors during file operations.
from fastapi import FastAPI, File, UploadFile
import uvicorn
import shutil
import os
app = FastAPI()
# Ensure the 'files' directory exists
os.makedirs("files", exist_ok=True)
@app.post("/uploadandsave/")
async def upload_and_save_file(file: UploadFile = File(...)):
file_location = f"files/{file.filename}"
with open(file_location, "wb+") as file_object:
shutil.copyfileobj(file.file, file_object)
return {"message": f"File '{file.filename}' saved at '{file_location}'"}
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)Uploading Many Files
What if you need to upload several files at once? FastAPI supports this by allowing you to define a parameter as a list of UploadFile.
Each file in the list will be an UploadFile object, which you can then process individually.
from fastapi import FastAPI, File, UploadFile
from typing import List
import uvicorn
app = FastAPI()
@app.post("/uploadmultiple/")
async def create_upload_files(files: List[UploadFile] = File(...)):
uploaded_filenames = [file.filename for file in files]
return {"filenames": uploaded_filenames, "message": "Files received!"}
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)Saving Multiple Uploads
Similar to single files, you can iterate through the list of UploadFile objects and save each one. This is useful for photo galleries or document uploads.
Always ensure proper error handling and secure file storage practices in a real application.
from fastapi import FastAPI, File, UploadFile
from typing import List
import uvicorn
import shutil
import os
app = FastAPI()
# Ensure the 'files' directory exists
os.makedirs("files", exist_ok=True)
@app.post("/uploadandsavemultiple/")
async def upload_and_save_multiple_files(files: List[UploadFile] = File(...)):
saved_files = []
for file in files:
file_location = f"files/{file.filename}"
with open(file_location, "wb+") as file_object:
shutil.copyfileobj(file.file, file_object)
saved_files.append(file.filename)
return {"message": f"Successfully uploaded: {', '.join(saved_files)}"}
if __name__ == "__main__":
uvicorn.run(app, host="0.0.0.0", port=8000)Form & File Check
You've learned about handling form data and file uploads. Let's test your understanding!
Lesson Summary
Great job! In this lesson, you mastered how to handle traditional form data and robust file uploads in FastAPI.
- We used
Form(...)for simple key-value form fields. - We explored
UploadFileandFile(...)for single and multiple file uploads. - You learned to save uploaded files to your server.
These techniques are crucial for building interactive web applications. Keep practicing!
Frequently asked questions
Is the “Form Data & File Uploads” lesson free?
Yes — the full text of “Form Data & File Uploads” is free to read here on the web, and the FastAPI Backend Development Bootcamp course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the FastAPI Backend Development Bootcamp course, upgrade to CoddyKit PRO.
What will I learn in “Form Data & File Uploads”?
Handle traditional HTML form data and implement file uploads using FastAPI's built-in capabilities. You practise FastAPI Backend Development Bootcamp with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start FastAPI Backend Development Bootcamp?
No prior experience is required. FastAPI Backend Development Bootcamp on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Form Data & File Uploads” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this FastAPI Backend Development Bootcamp lesson?
Yes. Every FastAPI Backend Development Bootcamp lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.