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Build a Secure File Sharing Web App with Python & Flask (Step-by-Step)

#python #beginners #tutorial #flask

In this tutorial, we’ll build a simple but powerful file-sharing web app using Python and Flask.

Users will be able to:

Upload files

Download shared files

Delete files

View file metadata

Access a simple API endpoint

By the end, you'll have a mini Dropbox-style file sharing tool running locally.

Project source code:

👉 https://github.com/rogers-cyber/python-tiny-tools/tree/main/77-File-sharing-web-app

Final Result

Your app will include:

• File upload interface
• Download links
• File size + upload date
• Delete button
• REST API for file list

Step 1 — Install Dependencies

First install Flask.

pip install flask
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Flask is a lightweight Python framework perfect for building small web tools quickly.

Step 2 — Create the Project File

Create a file called:

fileshare_pro.py
Step 3 — Import Required Libraries

Start by importing the modules we need.

import os
import uuid
import hashlib
from datetime import datetime
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And import Flask components:

from flask import (
    Flask,
    render_template_string,
    request,
    redirect,
    url_for,
    send_from_directory,
    abort
)
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What these do
Module Purpose
os file operations
uuid generate unique IDs
hashlib create file hashes
datetime store upload time
Flask web server framework
Step 4 — App Configuration

Next we configure the app.

APP_NAME = "FileShare PRO"
APP_VERSION = "1.0.0"

UPLOAD_FOLDER = "shared_files"
MAX_FILE_SIZE = 1024 * 1024 * 500
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This sets:

App name

Version

Upload folder

500MB max file size

Create the folder if it doesn't exist:

os.makedirs(UPLOAD_FOLDER, exist_ok=True)

Initialize Flask:

app = Flask(__name__)
app.config["UPLOAD_FOLDER"] = UPLOAD_FOLDER
app.config["MAX_CONTENT_LENGTH"] = MAX_FILE_SIZE
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Step 5 — Create an In-Memory Database

We’ll store uploaded files in a Python dictionary.

files_db = {}
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Each file will store:

{
id
name
path
size
hash
date
}
Step 6 — Generate Unique File IDs

Each file gets a short unique ID.

def generate_id():
    return str(uuid.uuid4())[:8]
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Example ID:

a91b32f0

This makes file URLs shorter and easier to share.

Step 7 — Create File Hash Function

We generate a hash checksum for each file.

def hash_file(path):

    md5 = hashlib.md5()

    with open(path, "rb") as f:
        for chunk in iter(lambda: f.read(4096), b""):
            md5.update(chunk)

    return md5.hexdigest()
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Why?

• Detect duplicate files
• Verify file integrity

Step 8 — Calculate File Size

We display file sizes in MB.

def get_file_size(path):
    return round(os.path.getsize(path) / 1024 / 1024, 2)
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Example output:

12.45 MB
Step 9 — Create the Web Interface

Instead of separate HTML files, we embed the template directly.

PAGE = """
<!DOCTYPE html>
<html>
<head>
<title>{{app_name}}</title>
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The interface includes:

Upload form

File table

Download links

Delete buttons

Example upload form:

<form method="POST" enctype="multipart/form-data">
<input type="file" name="file" required>
<button type="submit">Upload File</button>
</form>
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Example file table:

<table>
<tr>
<th>Name</th>
<th>Size</th>
<th>Date</th>
<th>Download</th>
<th>Delete</th>
</tr>
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Flask will dynamically populate this using Jinja:

{% for id,file in files.items() %}
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Step 10 — Create the Main Route

Now we create the homepage.

@app.route("/", methods=["GET", "POST"])
def index():
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If a file is uploaded:

if request.method == "POST":

    f = request.files["file"]

    if not f:
        return redirect("/")
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Generate a unique ID.

file_id = generate_id()
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Save the file.

filename = f.filename
path = os.path.join(app.config["UPLOAD_FOLDER"], file_id + "_" + filename)

f.save(path)
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Store metadata.

files_db[file_id] = {
    "name": filename,
    "path": path,
    "size": get_file_size(path),
    "hash": hash_file(path),
    "date": datetime.now().strftime("%Y-%m-%d %H:%M")
}
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Reload the page.

return redirect("/")
Step 11 — Download Files

Next create a download route.

@app.route("/download/<file_id>")
def download(file_id):
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Get the file from our database.

file = files_db.get(file_id)

if not file:
    abort(404)
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Send the file to the browser.

return send_from_directory(directory, filename, as_attachment=True)
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This triggers a download prompt.

Step 12 — Delete Files

Users can remove files.

@app.route("/delete/<file_id>")
def delete(file_id):
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Locate the file.

file = files_db.get(file_id)

if not file:
    abort(404)
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Delete it from disk.

os.remove(file["path"])
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Remove it from memory.

files_db.pop(file_id, None)
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Redirect back to homepage.

Step 13 — Create an API Endpoint

You can also expose the data via API.

@app.route("/api/files")
def api_files():
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Return JSON.

return {
    "app": APP_NAME,
    "version": APP_VERSION,
    "files": files_db
}
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Example response:

{
  "app": "FileShare PRO",
  "version": "1.0.0",
  "files": {...}
}
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Step 14 — Run the Server

Start the application.

if __name__ == "__main__":

    print(f"{APP_NAME} v{APP_VERSION} starting...")
    print("Open browser: http://127.0.0.1:5000")

    app.run(host="0.0.0.0", port=5000)
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Run it:

python fileshare_pro.py
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Open your browser:

http://127.0.0.1:5000
Features Recap

Your app now supports:

• File uploads
• Download links
• File deletion
• Upload timestamps
• File hashing
• Simple REST API

All in ~150 lines of Python.

Possible Improvements

Want to turn this into a production-level SaaS tool?

Add:

• user authentication
• cloud storage (S3)
• file expiration
• shareable public links
• drag-and-drop upload
• database (SQLite/PostgreSQL)
• file previews

Source Code

Full project:

👉 https://github.com/rogers-cyber/python-tiny-tools/tree/main/77-File-sharing-web-app

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