python_catchup_2024/3_advanced_classes.py

"""
Now that we know the basics of classes, variables, and functions, we will move on to more
abstract ideas.

I'm also going to introduce type hinting; this reduces ambiguity and improves readability.

Key Concepts:
    **Encapsulation** is the concept of grouping related data and methods within a 
    class and restricting access to them to control how they are used.
    
    **Access Modifiers** are used to determine who/what can access a certain attribute or method.
    
    - **Public**: Accessible from any part of the code. Used for attributes and methods intended to be part 
      of the class's interface for external use.
     
    - **Protected**: Intended for internal use within the class and its subclasses. "_value" represents it.
      Useful for attributes/methods that should be accessible in subclasses but not publicly.
     
    - **Private**: Only accessible within the class, represented by "__value". Useful for securing sensitive
      data or internal methods that should not be altered externally.
     
    IMPORTANT: Python does not strictly enforce access control, so these conventions mainly serve as guidelines.
"""

# This is the abstraction library in Python
from abc import ABC, abstractmethod
# Type hinting, not needed but reduces ambiguity. Note: not enforced at runtime.
from typing import Optional  

# An abstract class, provides a blueprint for other classes to inherit.
class Shape(ABC):  
    
    # This method is required in all subclasses, ensuring they provide their own area calculation.
    @abstractmethod
    def area(self) -> float: 
        """Implemented to ensure each subclass contains this method."""
        

class Rectangle(Shape):
    def __init__(self, width: float, height: float):
        # A private attribute to store width.
        self.__width = width 
        # A private attribute to store height.
        self.__height = height  

    # This allows access to the private 'width' attribute in a controlled way.
    @property  
    def width(self) -> float:
        return self.__width

    # This allows you to set the value of 'width' after initialization.
    @width.setter  
    def width(self, value: float):
        if value <= 0:
            raise ValueError("Width must be positive.")
        self.__width = value

    # This allows access to the private 'height' attribute in a controlled way.
    @property 
    def height(self) -> float:
        return self.__height

    # This allows you to set the value of 'height' after initialization.
    @height.setter  
    def height(self, value: float):
        if value <= 0:
            raise ValueError("Height must be positive.")
        self.__height = value

    def area(self) -> float:
        # Calculates the area of the rectangle.
        return self.__width * self.__height  

    def set_dimensions(self, width: Optional[float] = None, height: Optional[float] = None):
        if width is not None:
            # Sets 'width' using the setter.
            self.width = width 
        if height is not None:
            # Sets 'height' using the setter.
            self.height = height  

rect = Rectangle(5, 10)

# Prints the area of the rectangle (5 * 10 = 50).
print(rect.area())

# Updates 'width' using the setter, height remains the same.
rect.set_dimensions(width=8)

# Prints the new area of the rectangle (8 * 10 = 80).
print(rect.area())