Why file operations are common in FastAPI

Introduction

File operations let your FastAPI app save, read, and manage files like images or documents. This helps your app handle user uploads and serve files easily.

When users upload profile pictures or documents

To save logs or reports generated by the app

To serve static files like images or PDFs

When you need to read configuration or data files

To store temporary files during processing

Syntax

FastAPI

from fastapi import FastAPI, File, UploadFile

app = FastAPI()

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

Use UploadFile to handle file uploads efficiently.

Always use async functions with await when reading files in FastAPI.

Examples

This example reads the uploaded file and returns its size.

FastAPI

from fastapi import FastAPI, File, UploadFile

app = FastAPI()

@app.post("/uploadfile/")
async def upload(file: UploadFile = File(...)):
    contents = await file.read()
    return {"file_size": len(contents)}

This example serves a static file to the user.

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get("/getfile/")
def get_file():
    return FileResponse("./files/example.pdf")

Sample Program

This FastAPI app lets users upload files. It saves each file in a folder called 'uploaded_files'. It returns a message confirming the file was saved.

FastAPI

from fastapi import FastAPI, File, UploadFile
import os

app = FastAPI()

UPLOAD_DIR = "./uploaded_files"
os.makedirs(UPLOAD_DIR, exist_ok=True)

@app.post("/upload/")
async def upload_file(file: UploadFile = File(...)):
    file_location = os.path.join(UPLOAD_DIR, file.filename)
    contents = await file.read()
    with open(file_location, "wb") as f:
        f.write(contents)
    return {"info": f"File '{file.filename}' saved at '{file_location}'"}

Important Notes

Always check file size and type to keep your app safe.

Use UploadFile instead of raw bytes for better performance with large files.

Make sure the folder to save files exists or create it before saving.

Summary

File operations let FastAPI apps handle user files easily.

Use UploadFile and async reading for efficient uploads.

Saving and serving files is common for many web app features.