Mastering File Uploads in Flask: A Step-by-Step Guide
Kosal Ang
Tue Mar 19 2024
File uploads are a common feature in web applications, allowing users to share images, documents, or other types of files. Flask, a lightweight and flexible web framework for Python, provides easy-to-use tools for handling file uploads securely. In this article, we'll walk through the process of implementing file uploads in a Flask application, covering everything from setting up the application to handling file uploads and ensuring security.
Setting up the Flask Application
To get started, make sure you have Flask installed. If not, you can install it via pip:
1pip install Flask 2
Next, create a basic Flask application with a route to render an HTML form for file uploads.
1from flask import Flask, render_template, request 2 3app = Flask(__name__) 4 5@app.route('/') 6def index(): 7 return render_template('index.html') 8 9if __name__ == '__main__': 10 app.run(debug=True) 11
Creating the HTML Form
In your HTML template (templates/index.html), create a form to allow users to upload files:
1<!DOCTYPE html> 2<html> 3<head> 4 <title>File Upload</title> 5</head> 6<body> 7 <h2>Upload File</h2> 8 <form action="/upload" method="post" enctype="multipart/form-data"> 9 <input type="file" name="file"> 10 <input type="submit" value="Upload"> 11 </form> 12</body> 13</html> 14
Handling File Uploads in Flask
Add a route in your Flask application to handle file uploads and save the uploaded file securely:
1import os 2from flask import flash, redirect 3from werkzeug.utils import secure_filename 4 5UPLOAD_FOLDER = 'uploads' 6ALLOWED_EXTENSIONS = {'txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif'} 7 8app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER 9 10def allowed_file(filename): 11 return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS 12 13@app.route('/upload', methods=['POST']) 14def upload_file(): 15 if 'file' not in request.files: 16 flash('No file part') 17 return redirect(request.url) 18 file = request.files['file'] 19 if file.filename == '': 20 flash('No selected file') 21 return redirect(request.url) 22 if file and allowed_file(file.filename): 23 filename = secure_filename(file.filename) 24 file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename)) 25 return 'File uploaded successfully' 26 else: 27 return 'Invalid file format' 28
Ensuring Security
Ensure that you handle uploaded files securely by validating file extensions, renaming files, and storing them in a secure location. Use the secure_filename() function from the Werkzeug utility library to secure filenames.
Conclusion
With Flask, implementing file uploads in your web application is straightforward and secure. By following the steps outlined in this guide, you can enable users to upload files easily while ensuring that your application remains robust and protected against potential security threats. Whether you're building a photo-sharing platform, a document management system, or any other web application that requires file uploads, Flask provides the tools you need to get the job done efficiently and securely.
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