Attributes Annotations

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)


              1234567891011121314151617181920212223
            
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;

War alles klar?

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Abschnitt 2. Kapitel 3

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