# isinstance()
The `isinstance()` (is instance) is a Python built-in function that checks object is an instance of a certain class and return the bool value (`True` or `False`). This function takes 2 arguments: **instance** and **class**:

print(isinstance(662, int))
print(isinstance(25.3, int))

You can use this function to check your instances:

class User:
  pass

user = User()

print(isinstance(user, User))

# issubclass()
The `issubclass()` (is subclass) is a Python built-in function that checks class is a Child of another class:

class First:
    pass

class Second(First):
    pass

class Third(Second):
    pass

print(issubclass(Second, First))
print(issubclass(Third, First))

The `issubclass()` function works with **classes** only. If you want to check the instance, use the `type()` function inside the `issubclass()`:

class A:
    pass

class B(A):
    pass

instance = B()

print(issubclass(type(instance), A))

Let's start! The Object-Oriented Programming basic concepts are waiting for you here! In this section, you will get acquainted with the most important concepts for understanding Object-Oriented Programming.

Inheritance - the first of the OOP principles. The entities can be inherited from other ones. You learn how it works in code here.

Inheritance - the second of the OOP principles. The attributes and methods can be closed inside the class and used by the class only. Here you learn how to code with different access modifiers.

Polymorphism and abstraction are the third and fourth of the OOP principles. These principles are not easy to understand. Here you will get to know them in the simplest ways.

The magic methods make sandbox from Python. It's a unique Python tool you can't see in other languages. Here you learn how to use these methods and about the flexibility that they bring to Python.