Added Constructor in Python Documentation

docs/python/python-constructor.md

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+---
+id: python-constructor
+title: Python Constructor
+sidebar_label: Python Constructor #displays in sidebar
+description: Learn about constructors in Python OOP, including the __init__ method, types of constructors, and real-world use cases.
+sidebar_position: 19
+tags:
+  [
+    Python,
+    List in Python,
+    Introduction of python,
+    Python Syntax,
+    Variables,
+    Operators,
+    Type Casting,
+    String,
+    Tuple in Python
+    Array in Python
+    Functions in Python
+    Recursion in Python
+    Opps in Python
+  ]
+---
+
+# Constructor in Python
+
+In Python, a **constructor** is a special method used to initialize the newly created object of a class. It is called automatically when a new object is created.
+
+The most commonly used constructor in Python is the `__init__()` method.
+
+---
+
+## What is a Constructor?
+
+A **constructor** is a special method in a class that is automatically called when an object is instantiated. It allows you to define and initialize the attributes of the object.
+
+```python
+class Person:
+    def __init__(self, name, age):
+        self.name = name
+        self.age = age
+
+# Creating an object
+p1 = Person("Alice", 25)
+
+print(p1.name)  # Output: Alice
+print(p1.age)   # Output: 25
+````
+
+In the above example, `__init__()` is the constructor. It takes `name` and `age` as parameters and assigns them to the object's attributes.
+
+---
+
+## Syntax of `__init__()` Constructor
+
+```python
+def __init__(self, parameters):
+    # initialization code
+```
+
+* `self` refers to the current instance of the class.
+* You can pass additional parameters to set initial values for the object.
+
+---
+
+## Types of Constructors in Python
+
+### 1. Default Constructor
+
+A constructor that takes only the `self` argument.
+
+```python
+class Demo:
+    def __init__(self):
+        print("This is a default constructor")
+
+obj = Demo()
+```
+
+### 2. Parameterized Constructor
+
+A constructor that takes additional arguments to initialize the object.
+
+```python
+class Student:
+    def __init__(self, name, grade):
+        self.name = name
+        self.grade = grade
+
+s1 = Student("Ravi", "A")
+print(s1.name)   # Output: Ravi
+print(s1.grade)  # Output: A
+```
+
+---
+
+## Constructor with Default Values
+
+You can also define default values for constructor parameters.
+
+```python
+class Car:
+    def __init__(self, brand="Tesla"):
+        self.brand = brand
+
+car1 = Car()
+car2 = Car("BMW")
+
+print(car1.brand)  # Output: Tesla
+print(car2.brand)  # Output: BMW
+```
+
+---
+
+## Constructor in Inheritance
+
+When using inheritance, the constructor of the base class can be called using `super()`.
+
+```python
+class Animal:
+    def __init__(self, species):
+        self.species = species
+
+class Dog(Animal):
+    def __init__(self, species, name):
+        super().__init__(species)
+        self.name = name
+
+d = Dog("Mammal", "Buddy")
+print(d.species)  # Output: Mammal
+print(d.name)     # Output: Buddy
+```
+
+---
+
+## Real-World Use Case: Managing a Library System
+
+### Use Case: Library Book Management
+
+Suppose you're building a **Library Management System** where each book has the following data: title, author, and availability status.
+
+A constructor helps **initialize** the book’s data automatically when a book object is created.
+
+```python
+class Book:
+    def __init__(self, title, author, available=True):
+        self.title = title
+        self.author = author
+        self.available = available
+
+    def display_info(self):
+        status = "Available" if self.available else "Checked Out"
+        print(f"{self.title} by {self.author} - {status}")
+
+# Creating books
+book1 = Book("1984", "George Orwell")
+book2 = Book("The Alchemist", "Paulo Coelho", available=False)
+
+book1.display_info()   # Output: 1984 by George Orwell - Available
+book2.display_info()   # Output: The Alchemist by Paulo Coelho - Checked Out
+```
+
+### Why Constructor is Important Here?
+
+* Ensures every book created has all the necessary data.
+* Automatically sets a default availability status (e.g., available = True).
+* Prevents manual initialization after creating the object.
+* Keeps the code clean, consistent, and modular.
+
+Without a constructor, you'd have to write multiple lines of code every time a book is created, which can lead to errors and duplication.
+
+---
+
+## Summary
+
+* Constructors are used to initialize object properties at the time of creation.
+* Python uses the `__init__()` method as a constructor.
+* Constructors can be default, parameterized, or inherited.
+* They improve code organization and reduce repetition.
+* Real-world use cases like Library Systems, Inventory Management, User Registration, etc., rely heavily on constructors for clean initialization.