Form Data & File Uploads in Python

From the FastAPI cheat sheet · Form Data & File Uploads · verified Jul 2026

Form Data & File Uploads

Receive form fields and uploaded files in endpoints.

python

from fastapi import FastAPI, File, Form, UploadFile

@app.post("/login/")
async def login(username: str = Form(), password: str = Form()):
    return {"username": username}

@app.post("/upload/")
async def upload(file: UploadFile):
    contents = await file.read()
    return {"filename": file.filename, "size": len(contents)}

💡 Use Form() for form fields and File()/UploadFile for file uploads — not Pydantic models

⚡ UploadFile streams to disk — use it for large files; bytes = File() loads into memory

📌 You cannot mix JSON body (Pydantic) with form/file data in the same endpoint

🟢 Install python-multipart for form/file support: pip install python-multipart

formsfilesupload

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