Before we dive into code, you need a development environment. First, install Python. You can download it from the official Python website (python.org). Choose the latest stable version. During installation, be sure to check the box that adds Python to your PATH environment variable. This allows you to run Python from your command line/terminal.

Next, choose a text editor or IDE. Popular choices for beginners include VS Code, Sublime Text, Atom, or even the built-in IDLE (though IDEs like VS Code often offer more features out-of-the-box). Download and install your chosen editor. For this lesson, we will assume you have downloaded Visual Studio Code. A text editor with syntax highlighting and code completion will be very helpful. If you choose VS Code, install the Python extension from the Marketplace. This will add helpful features such as auto-completion and debugging.

Python is known for its readability. Let's start with the basics:

• Variables: Store data. You don't need to declare the data type explicitly. Examples:
  python name = "Alice" age = 30 is_active = True
• Data Types:
  • str (string): Text, e.g., "Hello"
  • int (integer): Whole numbers, e.g., 10
  • float (floating-point): Decimal numbers, e.g., 3.14
  • bool (boolean): True or False
• Operators: Perform actions. Examples:
  python # Arithmetic sum_result = 10 + 5 product = 3 * 4 division = 10 / 2 # Result is a float (5.0) remainder = 10 % 3 # Remainder of the division (1) # Comparison is_equal = (5 == 5) # True is_greater = (10 > 5) # True
• Control Flow:
  • if/else statements: Execute code conditionally.
    python age = 20 if age >= 18: print("You are an adult.") else: print("You are a minor.")
  • for loops: Iterate over a sequence (e.g., a list).
    python fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit)
  • while loops: Repeat code as long as a condition is true.
    python count = 0 while count < 3: print(count) count += 1

Python provides several built-in data structures:

• Lists: Ordered, mutable (changeable) collections of items. Defined using square brackets [].
  python my_list = [1, 2, 3, "apple", True] print(my_list[0]) # Access the first element (1) - lists are zero-indexed my_list.append(4) # Add an element to the end print(my_list)
• Dictionaries: Unordered collections of key-value pairs. Defined using curly braces {}.
  python my_dict = {"name": "Bob", "age": 25, "city": "New York"} print(my_dict["name"]) # Access the value associated with the key "name" ("Bob") my_dict["occupation"] = "Developer" # Add a new key-value pair print(my_dict)

Flask is a lightweight web framework written in Python. It's perfect for beginners and allows you to build web applications easily. First, install Flask using pip (the Python package installer). Open your terminal/command prompt and type: pip install flask

Now, let's create a simple "Hello, World!" Flask application. Create a new Python file (e.g., app.py) and add the following code:

from flask import Flask

app = Flask(__name__)

@app.route("/")  # This is a route decorator.  It binds a URL (/) to a function.
def hello_world():
    return "Hello, World!"

if __name__ == "__main__":
    app.run(debug=True) # Run the app.  debug=True is helpful during development.

• from flask import Flask: Imports the Flask class.
• app = Flask(__name__): Creates a Flask application instance.
• @app.route("/"): A decorator that tells Flask which URL should trigger the hello_world function.
• def hello_world():: The function that will be executed when the user visits the root URL (/).
• return "Hello, World!": Returns the text to display in the browser.
• app.run(debug=True): Runs the development server. debug=True provides useful error messages during development.

Save the file, open your terminal, navigate to the directory where you saved the file, and run it with: python app.py. Open your web browser and go to http://127.0.0.1:5000/ (or whatever address is printed by the terminal). You should see "Hello, World!" displayed in your browser. Congratulations, you've created your first web app!