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Days-19-22.md

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+### **Day 19: Introduction to Object-Oriented Programming (OOP)**
+Object-Oriented Programming is a programming paradigm that uses objects to represent real-world entities.
+
+- **Classes and Objects:**
+  - Classes define blueprints for creating objects.
+  - Objects are instances of classes.
+- **Attributes and Methods:**
+  - Classes can have attributes (data) and methods (functions) that define their properties and behavior.
+
+**Example of creating a simple class and an object:**
+```python
+# Define a simple class
+class Dog:
+    def __init__(self, name):
+        self.name = name
+
+    def bark(self):
+        print(f"{self.name} says woof!")
+
+# Create an object (instance) of the Dog class
+my_dog = Dog("Buddy")
+my_dog.bark()  # Call the bark method on the object
+```
+
+### **Day 20: Class Attributes and Methods**
+Classes can have attributes and methods that define their behavior.
+
+- **Class Attributes:**
+  - Class attributes are shared among all instances of the class.
+- **Instance Attributes:**
+  - Instance attributes are specific to individual objects.
+- **Methods:**
+  - Methods are functions defined within a class.
+
+**Example of class attributes and methods:**
+```python
+class Circle:
+    def __init__(self, radius):
+        self.radius = radius
+
+    def area(self):
+        return 3.14159 * self.radius**2
+
+    def circumference(self):
+        return 2 * 3.14159 * self.radius
+
+my_circle = Circle(5)
+print(f"Area: {my_circle.area()}")
+print(f"Circumference: {my_circle.circumference()}")
+```
+
+### **Day 21: Inheritance**
+Inheritance allows you to create new classes that inherit attributes and methods from existing classes.
+
+- **Parent Class (Superclass):**
+  - The parent class defines common attributes and methods.
+- **Child Class (Subclass):**
+  - The child class inherits from the parent class and can have additional attributes and methods.
+
+**Example of inheritance:**
+```python
+# Parent class
+class Animal:
+    def __init__(self, name):
+        self.name = name
+
+    def speak(self):
+        pass
+
+# Child class inheriting from Animal
+class Dog(Animal):
+    def speak(self):
+        return f"{self.name} says woof!"
+
+my_dog = Dog("Buddy")
+print(my_dog.speak())  # Calls the speak method of the Dog class
+```
+
+### **Day 22: Polymorphism**
+Polymorphism allows objects of different classes to be treated as objects of a common superclass.
+
+- **Common Superclass:**
+  - Create a common superclass that defines shared methods or attributes.
+- **Subclasses with Different Implementations:**
+  - Subclasses provide their own implementations of methods.
+
+**Example of polymorphism:**
+```python
+# Common superclass
+class Shape:
+    def area(self):
+        pass
+
+# Subclasses with different implementations of area
+class Circle(Shape):
+    def __init__(self, radius):
+        self.radius = radius
+
+    def area(self):
+        return 3.14159 * self.radius**2
+
+class Rectangle(Shape):
+    def __init__(self, width, height):
+        self.width = width
+        self.height = height
+
+    def area(self):
+        return self.width * self.height
+
+shapes = [Circle(5), Rectangle(4, 6)]
+
+for shape in shapes:
+    print(f"Area: {shape.area()}")
+```
+
+Object-Oriented Programming (OOP) is a fundamental concept in Python and many other programming languages. It allows you to model real-world entities, promote code organization, and enhance code reusability. Practice with these examples to become proficient in using OOP principles in Python.