Applications of the PYTHON PYFlask Web Server



The basics of HTTP, HTML, and Web Applications.

A note on Post and GET methods of FORM Submission:

A note about Web Servers in our PYTHON Application frameworks:

Flask and Django are both popular web frameworks in Python, but they serve different purposes and are typically used in different scenarios.
They share some common concepts and features as web frameworks. Understanding how they differ and their respective strengths can help in choosing the right tool for a specific project.


Flask is classified as a microframework. It is lightweight and modular, making it highly customizable.
Flask provides the basics to get a web application running and leaves the rest to the developer or third-party extensions.
Flexibility: Due to its minimalistic and modular approach, Flask gives developers a lot of flexibility in terms of how they structure their applications. It doesn't enforce any dependencies or project layout.
Suitability: It's well-suited for smaller projects or when a lot of customization and control over components is desired. It's also commonly used for creating RESTful APIs.


Batteries-included Framework: Django follows the "batteries-included" philosophy. This means it comes with a wide range of built-in features, including an ORM (Object-Relational Mapper), admin panel, and authentication support.
MVC Pattern: Django follows the Model-View-Template (MVT) pattern, which is similar to the Model-View-Controller (MVC) pattern. It has a more structured approach compared to Flask, with a set project structure and flow.
Suitability: Django is often chosen for larger applications or projects where a lot of built-in functionalities (like an admin interface, user authentication, database schema migrations, etc.) are beneficial.

Comparing Flask and Django

Design Philosophy: Flask offers simplicity and flexibility, while Django provides a more holistic approach with more out-of-the-box features.
Learning Curve: Flask generally has a gentler learning curve due to its simplicity. Django, with its many features, can be more overwhelming to new developers.
Community and Ecosystem: Both have strong communities and ecosystems, but Django's larger feature set means it has a more extensive ecosystem of built-in tools.
Use Cases: Flask is often preferred for microservices, simple web applications, or when integrating with technologies like machine learning libraries.
Django is typically chosen for more complex, database-driven web applications, especially when rapid development and built-in features are required.

Interrelation in Concept, Not in Use

While you wouldn't use Flask and Django together in a single project, understanding both can be beneficial. They share common web development concepts like URL routing, request and response handling, and template rendering.
Skills learned in one framework can often be applied to the other in a broader sense. For instance, understanding Flask's routing and view functions can help grasp Django's view system, and vice versa.
In summary, while Flask and Django are separate tools for web development in Python, they both contribute to a Python web developer's toolkit. The choice between them depends on the specific requirements of the project, the scale of the application, and the preference or familiarity of the development team.

A quick introduction to building the HTML Document Object Model:

<html> <head> <title> Peter's Great Page </title> </head>

<body bgcolor="red"> <h1><font color='yellow'>Welcome to our Web Application</font></h1> <h3><font color='pink'>Here you can find all the information you want about Brown Bear, Cony, Moon, Karen, Sally, and all the other beloved Line Characters</font></h1>
<div>Here is a Div Tag</div>
<form action=''> <input type='text' name='line_character_name'/>
<input type='submit' value = 'Click Here'/> </form>
<a href=''>Divvy's Day at Work</a>
<img width='100' src='brownbear.jpg'/> </body>

PYFlask Lab Learning Outcomes:

A comprehensive overview of RESTful APIs and their key principles (Representational APIs)
The use of Flask in Python for building web applications and APIs
How to use Python Flask for frontend updates to a MongoDB database using web forms
How to build a web application using Flask that interfaces with a MongoDB database through user-friendly web forms.

Introduction to Using Postman in Flask Labs

What is Postman?
Postman is a popular API client that makes it easy for developers to create, share, test, and document APIs. It provides a user-friendly graphical interface for constructing requests, reading responses, and other API-related tasks. Postman supports various HTTP methods such as GET, POST, PUT, and DELETE, making it an invaluable tool for testing and interacting with web APIs, including those built with Flask.

Why Use Postman in Flask Labs?

1. **Simplified API Testing**: Postman provides a straightforward way to test Flask routes, especially those that handle different HTTP methods and complex data payloads.
2. **No Frontend Required**: It allows testing Flask APIs without the need for a frontend interface. This is particularly useful in early development stages or for backend-focused labs.
3. **Visualization of Responses**: Postman neatly presents API responses, including headers, status codes, and body content, making it easier for students to understand the outcomes of their API requests.
4. **Efficient Debugging**: By manipulating request parameters in Postman, students can efficiently debug and fine-tune their Flask applications.
5. **API Documentation and Collaboration**: Postman can generate and share documentation for APIs, aiding in collaborative projects and communication between frontend and backend teams.

How to Use Postman with Flask

**Step 1: Install Postman** - Download and install Postman from [the official website](
**Step 2: Run Your Flask Application** - Ensure your Flask application is running locally. For example, it might be running on `http://localhost:5000`.
**Step 3: Create a New Request in Postman** - Open Postman and create a new request. - Choose the appropriate HTTP method (GET, POST, etc.) that corresponds to the Flask route you want to test. - Enter the URL of your Flask route. For example, `http://localhost:5000/api/data`.
**Step 4: Configure Your Request (for POST, PUT methods)** - If you are testing routes that require data (like POST or PUT), you can add data in the 'Body' tab in Postman. - Choose the correct format (e.g., form-data, raw JSON) and input the necessary data.
**Step 5: Send the Request and Analyze the Response** - Click the 'Send' button to make the request to your Flask application. - Analyze the response that Postman displays. Look at the status code, response body, and headers for debugging and understanding the behavior of your API.
**Step 6: Iterate and Test Further** - Make modifications to your Flask app based on the results, and retest as needed.
#### Example Lab Exercise Using Postman
**Objective**: Test a Flask API that handles user registrations via a POST request.
- Students will create a Flask route `/register` that accepts POST requests with JSON data containing `username` and `password`. - Using Postman, students will construct a POST request with appropriate JSON data and send it to the Flask API. - Students will observe and analyze the response from the Flask API, including handling any errors or successful registrations.
This exercise allows students to understand how backend and frontend interact, the importance of HTTP methods, and how data is transmitted and received in a web application. Postman acts as a stand-in for a frontend client, making it a valuable tool for backend development and testing.

The TCP IP Network Mechanics of Post and Get:

Training Evolution 1:

Create a simple web application in Flask that echoes back form field input to introduce students to handling forms in Flask.
This lab will involve creating a basic Flask application with a form, and then processing and displaying the input received from the user.
Note: For this training evoluation, let’s work with Sublime Text Editor in the Command Prompt to go ‘hands-on’ with the low level implementation details:

Lab Exercise: Flask Application to Echo Form Input

Create a Flask web application with a form.
The application should display the input received from the form back to the user.
#### Step 1: Set Up Your Flask Application
First, ensure Flask is installed. You can install it using pip:
```bash ​pip install flask ```

Now, create a new Python file, let's call it ``, and set up your Flask application:

from flask import Flask, request, render_template_string
app = Flask(__name__)
@app.route('/') def index(): return ''' <form method="post" action="/echo"> <input type="text" name="text" placeholder="Enter some text" /> <input type="submit" value="Echo" /> </form> '''
@app.route('/echo', methods=['POST']) def echo(): user_input = request.form['text'] return f"You entered: {user_input}"
if __name__ == '__main__': ```
#### Step 2: Understand the Code
- The `index` function renders a simple HTML form with one text input and a submit button. - The form's action is set to `/echo`, and the method is `POST`. - The `echo` function handles the POST request to `/echo`. It extracts the text input from the form (`request.form['text']`) and displays it back to the user.

Step 3: Run Your Application

Run your application using the command:
```bash python ​
#### Step 4: Test the Application
- Open a web browser and navigate to `http://localhost:5000`. - Enter some text in the form and click the "Echo" button. - The application will display the entered text on a new page.
#### Additional Notes
- This application does not use external templates for simplicity. In a more complex application, it's recommended to use separate HTML files for templates. - Form validation and error handling are not included in this basic example but are important aspects to consider for more complex applications.
This lab is a fundamental introduction to handling forms in Flask and can be expanded upon for more advanced form handling, including validation, file uploads, and using templates.

Guessing Game PYFLASK with Forms program:

from flask import Flask, request, render_template_string, session import random from flask import redirect, url_for
app = Flask(__name__) app.secret_key = 'your_secret_key' # Replace 'your_secret_key' with a real secret key
@app.route('/', methods=['GET', 'POST']) def index(): # Initialize or reset the game if request.method == 'GET' or 'number' not in session: session['number'] = random.randint(1, 100) # Random number between 1 and 100 session['attempts'] = 0 return ''' <form method="post" action="/"> <p>Guess a number between 1 and 100:</p> <input type="number" name="guess" /> <input type="submit" value="Guess" /> </form> '''
else: # Process the guess guess = int(request.form['guess']) session['attempts'] += 1
if guess < session['number']: message = "Too low!" elif guess > session['number']: message = "Too high!" else: message = f"Correct! You guessed the number in {session['attempts']} attempts." session.pop('number', None) # Remove the number; restart the game return render_template_string(f"<p>{message}</p><a href='/'>Play again</a>")
return render_template_string(f''' <p>{message}</p> <form method="post" action="/"> <input type="number" name="guess" /> <input type="submit" value="Guess again" /> </form> ''')
if __name__ == '__main__':


- The basics of Flask and MongoDB integration to creating and handling web forms, - Updating the database based on user input.

Lab Outline: Building a Flask Web Application with MongoDB Integration

Lab 1: Introduction to Flask and MongoDB
1. **Overview of Flask** - What is Flask and its use cases - Flask's microframework architecture
2. **Introduction to MongoDB** - Basics of MongoDB - Advantages of using MongoDB with Flask
3. **Setting Up the Development Environment** - Installing Python and Flask - Setting up MongoDB - Useful tools (e.g., Robo 3T for MongoDB management)
Lab 2: Flask and MongoDB Integration
1. Flask-PyMongo - Introduction to Flask-PyMongo extension - Configuring Flask app to connect with MongoDB
2. **Basic Operations with MongoDB** - Creating a database and collections - CRUD operations in MongoDB using Flask
3. **Sample Application** - Building a simple Flask app to perform database operations
Lab 3: Introduction to Web Forms in Flask
1. **Understanding Web Forms** - Role of web forms in a web application - HTML forms and HTTP methods (GET vs POST)
2. **Flask-WTF Extension** - Using Flask-WTF for form handling - Form classes and field types
3. **Form Validation** - Server-side validation with Flask-WTF - Displaying form errors in templates

Lab 4: Building and Handling Forms in Flask
1. **Creating a Web Form** - Designing a form using HTML and Flask-WTF - Handling form submission in Flask
2. **Integrating Forms with Templates** - Rendering forms in Jinja2 templates - Styling forms with CSS
3. **Form Security** - CSRF protection in Flask-WTF - Best practices for secure form handling

Lab 5: Updating MongoDB with Flask Web Forms
1. **Form to MongoDB Integration** - Extracting data from form fields - Inserting and updating data in MongoDB
2. **Building a Complete Application** - Developing a Flask application where users can add, edit, and delete data in MongoDB via web forms
3. **Debugging and Testing** - Debugging Flask applications - Basic testing approaches for Flask and MongoDB

Lab 6: Advanced Topics and Best Practices
1. **Advanced Form Handling** - Dynamic forms - File upload and handling
2. **Scalability and Performance** - Scaling Flask applications with MongoDB - Performance considerations
3. **Security Best Practices** - Securing the Flask application - Secure MongoDB integration
4. **Deployment** - Deploying Flask applications on different platforms (e.g., Heroku, AWS)

Hands-On Lab Activities
By the end of the series, students will work on a project where they build a Flask web application that integrates with a MongoDB database and allows for CRUD operations through web forms.

Using the Secret Session KEY

In a Flask application, app.secret_key is a configuration value that sets the secret key for your application.
This key is critically important for some of Flask's functionalities, particularly for securely signing the session cookie and for the operation of extensions that use the session for storing information.

Here are a few points to understand about app.secret_key:
Session Management: Flask uses a client-side session, which means that the session data is stored in the client's browser as a cookie. This session cookie needs to be securely signed to prevent tampering. The app.secret_key is used to cryptographically sign the session cookies. When Flask decrypts the cookie on a subsequent request, it uses the secret key to validate the signature. If the signature doesn't match, indicating that the cookie has been tampered with, Flask rejects the cookie.
Security: The secret key should be kept secret. It should be a complex random value that is not easy to guess or derive. If an attacker were to know the secret key, they could potentially create and modify session cookies to perform actions as if they were other users.
Generating Secret Keys: It's important to generate a strong, unpredictable secret key. This can be achieved using a random number generator, cryptographic functions, or other secure means. Python's os.urandom() function, for instance, can be used to generate a strong secret key.
Environment Variables: Instead of hardcoding the secret key in the source code, it is often recommended to set it through an environment variable. This approach enhances security by keeping the key out of the source code, which might be shared or stored in less secure locations like version control systems.
Here's an example of how to generate a secure secret key in Python and use it in a Flask application:
pythonCopy code
import os
from flask import Flask

app = Flask(__name__)
app.secret_key = os.urandom(24) # Generates a random 24-byte key

In a production environment, you should ensure that the secret key remains the same across application restarts, which usually means setting it through an environment variable or a configuration file, rather than generating it on each start-up.

The PYTHONIC Calculator:

Give your Flask-based calculator application a Caribbean seaside motif using CSS, you'll want to incorporate design elements that evoke the sea, sand, and tropical environment.
Think about using colors like blue, green, sandy beige, and sun-bleached whites. You could also add graphical elements like palm trees, beaches, or waves. However, since this is a text-only environment, I'll focus on colors and basic styling that you can expand upon.
First, modify your HTML structure to include classes that you can target with your CSS:
```python def get_calculator_html(): html = ''' <!DOCTYPE html> <html> <head> <title>Caribbean Calculator</title> <style> body { font-family: Arial, sans-serif; background-color: #e0f7fa; /* light blue background */ color: #00695c; /* dark green text */ text-align: center; padding: 20px; } .container { background-color: #fff3e0; /* light sand color */ border-radius: 10px; display: inline-block; padding: 20px; box-shadow: 0px 0px 10px 0px #0003; } h1 { color: #f9a825; /* sun yellow */ } input, select { margin: 10px; padding: 5px; border-radius: 5px; border: 1px solid #00695c; } .result { color: #00796b; /* sea green */ font-size: 1.2em; margin-top: 20px; } </style> </head> <body> <div class="container"> <h1>Simple Calculator</h1> <form method="post" action="/calculator"> <input type="number" step="any" name="num1" placeholder="First Number" required> <input type="number" step="any" name="num2" placeholder="Second Number" required> <select name="operator"> <option value="+">+</option> <option value="-">-</option> <option value="*">*</option> <option value="/">/</option> </select> <input type="submit" value="Calculate"> </form> {% if result is not None %} <div class="result">Result: {{ result }}</div> {% endif %} </div> </body> </html> ''' return html ```
In this version of `get_calculator_html`:
- I've added a `<style>` section in the `<head>` to hold the CSS. - The CSS styles incorporate a Caribbean palette: light blue for the sky, dark greens for tropical foliage, a sun yellow for the heading, and sand-like colors for the background of the calculator. - The calculator itself is in a `.container` class, with a subtle box shadow to give it some depth. - The `.result` class is styled to make the result stand out.
These changes will give your calculator a Caribbean seaside feel. You can further enhance this by adding more detailed styling, images, or even animations as needed.

To run the Flask application provided earlier (the calculator), you'll need to have Python installed on your machine along with Flask. If you haven't installed Flask yet, you can do so using pip, Python's package installer. Here’s a step-by-step guide:
1. **Install Python**: Make sure you have Python installed on your computer. You can download it from [](
2. **Install Flask**: Open your terminal (Command Prompt, PowerShell, or Terminal app, depending on your operating system) and install Flask using pip: ``` pip install Flask ```
3. **Save Your Flask Application**: Copy the Flask application code into a file named `` (or any other name you prefer, but ensure it has a `.py` extension).
4. **Run the Application**: - Open your terminal and navigate to the directory where your `` file is located. You can use the `cd` command to change directories. - Run the application by typing: ``` python ``` or if your system requires it: ``` python3 ```
5. **Access the Application**: Once the application is running, open a web browser and go to `http://localhost:5000/calculator`. This will open the calculator interface provided by your Flask application.
6. **Stop the Application**: To stop the Flask server, go back to your terminal and press `Ctrl+C`.
Remember, the above instructions assume that you are running the application in a development environment on your local machine. Deploying a Flask application to a production environment would require additional steps and configurations.
In this updated version: - The `/calculator` route handles both GET and POST requests.
On a GET request, it displays the calculator interface,
On a POST request, it performs the calculation based on user input.
- The HTML form allows the user to input two numbers and select an operation (addition, subtraction, multiplication, division). - The result of the calculation is displayed after the form submission.
This code should work as a basic web-based calculator.

RESTful APIs and Flask in Python

Part 1: What are RESTful APIs?

REST stands for Representational State Transfer. It is an architectural style for designing networked applications. A RESTful API (Application Programming Interface) uses HTTP requests to GET, PUT, POST, and DELETE data.
RESTful APIs are stateless, meaning that each request from a client to a server must contain all the information needed to understand and process the request. The server does not store any information about the client between requests.
Key principles of REST include:
Client-Server Architecture: The client is responsible for the user interface and user experience, and the server is responsible for processing requests and managing resources.
Statelessness: Each request from a client to a server must contain all the information needed to understand and process the request.
Cacheability: Responses from the server can be cached by the client to improve performance.
Layered System: The architecture allows for layers of servers that can be added to improve scalability.

Part 2: Using RESTful APIs in Python with Flask

Flask is a lightweight and extensible web framework for Python.
It is designed to make it easy for developers to build web applications and APIs.
Flask is particularly well-suited for building RESTful APIs due to its simplicity and flexibility.
Here are the steps to create a simple RESTful API with Flask:
Install Flask: Use pip to install Flask: pip install flask
Create a Flask Application: Import Flask and create an instance of the Flask class.
Define Routes: Use the @app.route() decorator to define routes for your API. Each route corresponds to a specific resource.
Define HTTP Methods: For each route, define the HTTP methods (GET, PUT, POST, DELETE) that it should respond to.
Return JSON Responses: Use the jsonify() function to convert Python dictionaries into JSON responses.
Error Handling: Use the @app.errorhandler() decorator to define custom error handling.
In the next lecture, we will dive deeper into each of these steps and learn how to build a fully functional RESTful API with Flask.

Building Web Applications using the RESTFUL API Model.

Flask is a lightweight and extensible web framework for Python, designed to make it easy for developers to build web applications and APIs. It is known for its simplicity, flexibility, and a large and active community. Here are some of the key applications of Flask:
Web Applications
Flask is commonly used to create web applications, ranging from simple, small-scale projects to more complex web services. Its minimalistic design is particularly suited for projects where a lightweight and modular framework is advantageous
Developers often choose Flask for developing RESTful APIs because of its ability to create clean and pragmatic REST interfaces. Flask's modular design allows for the easy creation of endpoints that can serve data, interact with databases, and integrate with other services
Prototyping and MVPs
Flask is an excellent choice for prototyping and developing Minimum Viable Products (MVPs) due to its simplicity and rapid development capabilities. It allows for quick iteration and testing of new ideas
Static Websites
For projects that require a simple static website or a backend to feed a Single Page Application (SPA) or mobile app, Flask is a good choice. It performs well due to its smaller size and fewer layers
Integration with Cutting-edge Technologies
Flask is compatible with advanced technologies such as machine learning and cloud computing, making it a versatile choice for projects that require the integration of such technologies
Flexibility and Scalability
Flask's microframework nature means it can be used to grow a tech project quickly. It is ideal for apps that start small but have the potential to expand rapidly
Development and Testing
Flask includes a built-in development server and debugger, which facilitates local development and testing. It also has a built-in unit testing mechanism that allows for faster debugging and more stable development
Customization and Extensions
Due to its modular nature, Flask allows developers to add extensions and customize the framework to fit their specific needs. There is a wide range of community-maintained extensions available that add functionality to Flask applications
Educational Use
Flask's simplicity makes it an accessible framework for new developers and is often used for educational purposes to teach web development basics
Maintenance and Support
While Flask is versatile, companies using it may incur extra costs for supporting the technologies it interfaces with, especially as the application grows in complexity
In summary, Flask is a versatile web framework that is particularly well-suited for building lightweight web applications, RESTful APIs, and for use in prototyping and educational settings. Its simplicity and flexibility make it a popular choice among developers for a variety of projects

Python Flask Lab

Exercise 1: Hello World in Flask

Objective: This exercise will introduce students to the basics of Flask by creating a simple "Hello, World!" web application.
Install Flask using pip: pip install flask
Create a new Python file and import Flask: from flask import Flask
Create an instance of the Flask class: app = Flask(__name__)
Define a route for the home page of your web application that returns "Hello, World!":
def home():
return "Hello, World!"

Run your Flask application:
if __name__ == '__main__':

Open a web browser and navigate to http://localhost:5000 to see your "Hello, World!" message.

Exercise 2: Routing in Flask

Objective: This exercise will teach students how to create multiple routes in a Flask application.
Define a new route for a page called "About" that returns "This is the About page.":
def about():
return "This is the About page."

Run your Flask application and navigate to http://localhost:5000/about to see your About page.

Exercise 3: Templates in Flask

Objective: This exercise will teach students how to use templates in Flask to create dynamic web pages.
Create a new folder in your project directory called "templates".
Inside the "templates" folder, create a new HTML file called "home.html".
In "home.html", write some HTML code for a simple web page.
Modify the home route in your Flask application to render the "home.html" template:
from flask import render_template

def home():
return render_template('home.html')

Run your Flask application and navigate to http://localhost:5000 to see your dynamic home page.

Exhance the Flask program so that it includes a form where users can enter their name and then have that name displayed on a rendered HTML template, we'll need to make a few adjustments.
We'll add a form to the home.html template, handle the form submission in a new route, and then pass the entered name to another template which will display the name.
Here's how you can modify the Flask application:

Flask Application Code

from flask import Flask, render_template, request

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def home():
if request.method == 'POST':
name = request.form['name']
return render_template('greet.html', name=name)
return render_template('home.html')

if __name__ == '__main__':

In this code, the home route handles both GET and POST requests.
If it's a POST request (which occurs when the form is submitted), it captures the name from the form data and renders a new template, greet.html, passing the name to it.
If it's a GET request, it simply shows the home page with the form.

HTML Templates

You need two templates: home.html for the form and greet.html to display the user's name.
<!DOCTYPE html>
<form method="post" action="/">
<label for="name">Enter your name:</label>
<input type="text" id="name" name="name">
<input type="submit" value="Submit">

This is the home page template with a simple form.

<!DOCTYPE html>
<h1>Hello, {{ name }}!</h1>

This template takes the name passed from the home route and displays it.

Running the Application

Ensure both home.html and greet.html are saved in a folder named templates in the same directory as your
Run your Flask application using the command:
bashCopy code
Open a web browser and go to http://localhost:5000. Enter a name in the form and see the greeting with the entered name on submission.


This application uses POST method for form submission, which is a good practice for sending data.
Ensure that the templates directory is correctly named and located, as Flask looks for templates in a folder with this specific name.

Here's a simple Flask application with a few routes to demonstrate basic RESTful principles:

This code creates a basic RESTful API with Flask, allowing for CRUD (Create, Read, Update, Delete) operations on a simulated database represented by a Python dictionary.
The routes handle different HTTP methods (GET, POST, PUT, DELETE) and interact with the data accordingly.
This is a fundamental example to help you get started with Flask and RESTful API development.
# Import the Flask library
from flask import Flask, jsonify, request

# Create an instance of the Flask class
app = Flask(__name__)

# A simple database simulated with a dictionary
fake_db = {
"1": {"name": "Item 1", "description": "This is item 1"},
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