In Python, abstract base classes (ABCs) in the abc module define interfaces for subclasses to implement, enforcing polymorphism and preventing instantiation of incomplete classes. Use them for designing robust class hierarchies where specific methods must be overridden.

from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self):
        pass

class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        return self.width * self.height

# rect = Rectangle(5, 3)
# print(rect.area())  # 15
# Shape()  # Error: Can't instantiate abstract class

#python #OOP #classes #abc #inheritance

👉 @DataScience4

In Python, "Magic Methods" (also known as Dunder methods, short for "double underscore") are special methods that allow you to define how objects of your class behave with built-in functions and operators. While init handles object initialization, str and repr are crucial for defining an object's string representation.

str: Returns a "user-friendly" string representation of an object, primarily for human readability (e.g., when print() is called).
repr: Returns an "official" string representation of an object, primarily for developers, often aiming to be unambiguous and allow recreation of the object.

class Book:
    def init(self, title, author, year):
        self.title = title
        self.author = author
        self.year = year

    def str(self):
        return f'"{self.title}" by {self.author} ({self.year})'

    def repr(self):
        return f"Book('{self.title}', '{self.author}', {self.year})"

Creating an instance

my_book = Book("The Hitchhiker's Guide to the Galaxy", "Douglas Adams", 1979)

str is used by print()

print(my_book)

repr is used by the interpreter or explicitly with repr()

print(repr(my_book))

In collections, repr is used by default

bookshelf = [my_book, Book("Pride and Prejudice", "Jane Austen", 1813)]
print(bookshelf)

Output:

"The Hitchhiker's Guide to the Galaxy" by Douglas Adams (1979)
Book('The Hitchhiker\'s Guide to the Galaxy', 'Douglas Adams', 1979)
[Book('The Hitchhiker\'s Guide to the Galaxy', 'Douglas Adams', 1979), Book('Pride and Prejudice', 'Jane Austen', 1813)]

#Python #MagicMethods #DunderMethods #OOP #Classes #PythonTips #CodeExamples #StringRepresentation #ObjectOrientation #Programming

---
By: @DataScienceQ ✨

Python Tip: Mastering init and self in OOP! 🐍

When defining a class in Python, init is a special method (often called the constructor) that gets called automatically every time a new object (instance) of the class is created. It's used to set up the initial state or attributes of that object.

The self parameter is a convention and the first parameter of any instance method. It always refers to the instance of the class itself, allowing you to access its attributes and other methods from within the class.

class Car:
    def init(self, make, model, year):
        self.make = make    # Assign 'make' to the instance's 'make' attribute
        self.model = model  # Assign 'model' to the instance's 'model' attribute
        self.year = year    # Assign 'year' to the instance's 'year' attribute

    def get_description(self):
        return f"This is a {self.year} {self.make} {self.model}."

In the init method, self.make = make means "take the value passed in as make and assign it to the make attribute of this specific Car object."

Let's create some cars:

my_car = Car("Toyota", "Camry", 2020)
your_car = Car("Honda", "Civic", 2022)

print(my_car.get_description())
print(your_car.get_description())

Output:

This is a 2020 Toyota Camry.
This is a 2022 Honda Civic.

init ensures each object starts with its own data, and self connects you to that data!

#PythonTip #OOP #Classes #InitMethod #SelfKeyword #ObjectOriented #PythonProgramming
---
By: @DataScienceQ ✨

#include <iostream>
#include <vector>

int main() {
    std::vector<int> numbers;
    numbers.push_back(5);
    numbers.push_back(10);
    std::cout << "Vector size: " << numbers.size();
    return 0;
}

Vector size: 2

#34. .size()
Member function that returns the number of elements in a container like std::vector or std::string.

#include <iostream>
#include <vector>

int main() {
    std::vector<std::string> fruits = {"Apple", "Banana"};
    std::cout << "There are " << fruits.size() << " fruits.";
    return 0;
}

There are 2 fruits.

#35. .length()
A member function of std::string that returns its length. It's synonymous with .size().

#include <iostream>
#include <string>

int main() {
    std::string text = "C++";
    std::cout << "The length of the string is: " << text.length();
    return 0;
}

The length of the string is: 3

---
#CPP #STL #Algorithms

#36. #include <algorithm>
Includes the standard library algorithms, like sort, find, copy, etc.

#include <iostream>
#include <vector>
#include <algorithm> // Required for std::sort

int main() {
    std::vector<int> nums = {3, 1, 4};
    std::sort(nums.begin(), nums.end());
    std::cout << "Sorting is possible with <algorithm>.";
    return 0;
}

Sorting is possible with <algorithm>.

#37. std::sort()
Sorts the elements in a range (e.g., a vector).

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {50, 20, 40, 10, 30};
    std::sort(nums.begin(), nums.end());
    for(int n : nums) {
        std::cout << n << " ";
    }
    return 0;
}

10 20 30 40 50

#38. .begin()
Returns an iterator pointing to the first element in a container.

#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums = {100, 200, 300};
    auto it = nums.begin();
    std::cout << "First element: " << *it;
    return 0;
}

First element: 100

#39. .end()
Returns an iterator referring to the past-the-end element in the container.

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {1, 2, 3};
    // .end() points after the last element, used as a boundary
    std::cout << "Vector has elements until the end.";
    return 0;
}

Vector has elements until the end.

#40. #define
A preprocessor directive used to create macros or symbolic constants.

#include <iostream>
#define PI 3.14159

int main() {
    std::cout << "The value of PI is " << PI;
    return 0;
}

The value of PI is 3.14159

---
#CPP #OOP #Classes

#41. class
A keyword used to declare a class, which is a blueprint for creating objects.

#include <iostream>

class Dog {
public:
    void bark() {
        std::cout << "Woof!";
    }
};

int main() {
    Dog myDog;
    myDog.bark();
    return 0;
}

Woof!

#42. struct
Similar to a class, but its members are public by default.