Introduction to Flask

Flask is a lightweight and versatile web framework for Python that allows developers to build web applications quickly and efficiently. Flask is known for its simplicity, flexibility, and scalability, making it an excellent choice for both beginners and experienced developers.

Flask follows the WSGI (Web Server Gateway Interface) standard and is designed with simplicity in mind. It’s often referred to as a “micro” framework because it provides the essential tools required to build web applications without the complexities of larger frameworks like Django.

Key Features of Flask:

• Lightweight: Flask has minimal dependencies, ensuring better performance.
• Flexible: Developers can add third-party extensions as needed.
• Built-in Development Server: Includes a debugger and a development server.
• Jinja2 Templating Engine: Provides dynamic HTML page rendering.
• RESTful Routing: Easily create APIs using its routing mechanisms.

Installing Flask on Ubuntu

Installing Flask on Ubuntu is straightforward and can be done in multiple ways. Here are the recommended methods:

Method 1: Installing Flask using pip (Recommended)

This method is ideal for installing Flask in a virtual environment for better dependency management.

Step 1: Update System Packages

Run the following command to ensure your system packages are up to date:

sudo apt update && sudo apt upgrade -y

Step 2: Install Python and Pip

Ensure Python3 and pip are installed:

sudo apt install python3 python3-pip -y

Step 3: Install venv for Virtual Environment

To create isolated environments for your Flask projects:

sudo apt install python3-venv -y

Step 4: Create a Virtual Environment

Create a directory for your Flask project and set up a virtual environment:

mkdir flask_project
cd flask_project
python3 -m venv venv

Step 5: Activate the Virtual Environment

Activate the virtual environment with the following command:

source venv/bin/activate

Your command prompt should now start with (venv) indicating the virtual environment is active.

Step 6: Install Flask

Now install Flask using pip:

pip install flask

Step 7: Verify Installation

Check if Flask is successfully installed:

python3 -m flask --version

Method 2: Installing Flask via apt (Less Preferred)

This method is easier but may provide outdated versions.

sudo apt install python3-flask -y

This method is not ideal for building production-ready applications but may be useful for quick testing or learning purposes.

Creating a Simple Flask Application

Once Flask is installed, follow these steps to build a simple web application.

Step 1: Create a Python Script

Create a new Python file called app.py in your Flask project folder:

nano app.py

Step 2: Write Basic Flask Code

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, World! Welcome to Flask on Ubuntu!"

if __name__ == "__main__":
    app.run(debug=True)

Step 3: Run the Application

Execute the Flask application using:

python3 app.py

By default, Flask will run on http://localhost:5000.

Step 4: Access the Application

Open your web browser and visit:

http://localhost:5000

You should see: “Hello, World! Welcome to Flask on Ubuntu!”

Method 3: Installing Flask Using Docker (Optional)

For those working with containerized environments, installing Flask via Docker is also possible.

Step 1: Install Docker

sudo apt install docker.io

Step 2: Create a Dockerfile

FROM python:3.10-slim
WORKDIR /app
COPY . /app
RUN pip install flask
CMD ["python3", "app.py"]

Step 3: Build and Run the Docker Container

docker build -t flask_app .
docker run -p 5000:5000 flask_app

Common Flask Commands

• flask run: Starts the development server.
• flask shell: Opens a shell within the Flask app’s context.
• flask routes: Displays the defined routes in the application.

Best Practices for Flask Projects

1. Use Virtual Environments: Isolating dependencies ensures a stable development environment.
2. Follow MVC Structure: Keeping models, views, and controllers organized improves scalability.
3. Implement Environment Variables: For better security, store sensitive data like database credentials in .env files.
4. Use Flask Extensions: Extensions like Flask-SQLAlchemy, Flask-WTF, and Flask-Login simplify complex tasks.
5. Write Unit Tests: Ensure app reliability with unittest or pytest frameworks.

Conclusion

Flask is an excellent choice for developing web applications with Python. By following the steps outlined in this guide, you can confidently install Flask on Ubuntu and begin building robust web applications. Whether you’re a beginner or an experienced developer, Flask’s simplicity and flexibility make it a powerful tool for creating modern web solutions.