Using annotations starting with `@` symbol is a special way to define properties.

 - Write `@property` to define `get()` method;
 - Write `@attribute.setter` to define the `set()` method for the attribute.


We need to do that to explain to Python what these methods are going to be used for. 

class Cat:

  def __init__(self, name = 'Kitty', age = 1):
    self.name = name
    self.__age = age
    self.__number_of_legs = 4

  @property
  def age(self):
    return self.__age

  @age.setter
  def age(self, age):
    if isinstance(age, int) and 0<=age<=30:
      self.__age = age
    else:
      print('Invalid value of attribute age')

cat = Cat('Maggie', 3)
# Adding the wrong value
cat.age = -100 
cat.age = 5
print(cat.age)

## Note

 - First, define getter `@property` and after that – setter `@attribute.setter`;
 - Both methods have the same name, that is equal to the attribute name;
 - **Now, to access the private attribute `__age` outside the class, you can use the `cat.age` expression**;

The first step is to understand the key statements. Classes, objects, attributes, methods...

Encapsulation provides access to the methods and attributes of the class.

Inheritance's main idea is to use already defined classes and produce new ones by improving and extending some other classes.

This OOP principle allows the user to change the parent class functionality and adapt it to the children's class.