Python, Encapsulation / Data Hiding.

Question

#Sharing a code from Sololearn's Module:
class Pizza:
def __init__(self, toppings):
self.toppings = toppings
self._pineapple_allowed = False

@property
def pineapple_allowed(self):
return self._pineapple_allowed

@pineapple_allowed.setter
def pineapple_allowed(self, value):
if value:
password = input("Enter the password: ")
if password == "Sw0rdf1sh!":
self._pineapple_allowed = value
else:
raise ValueError("Alert! Intruder!")

pizza = Pizza(["cheese", "tomato"])
print(pizza.pineapple_allowed)
pizza.pineapple_allowed = True
print(pizza.pineapple_allowed)
#I am unable to understand the role of setter method here! My interpretation: The last 4th line of code creates an instance. The last third line refers to the pineapple_allowed(self) method which returns the False statement because of __init__. I am unable to understand the rest please help. Sorry if the question is lengthy! Thanks in Advance.

Answer 1

This lesson is not about classmethod, but Encapsulation / Data Hiding.
The Pizza class has an instance variable _pineapple_allowed.
Notice the underscore in the beginning that means it is a private variable that is not supposed to be changed directly from the outside. This is where python introduces the @property decorator. You have two functions with the same name (pineapple_allowed). The first one is the "getter" method whose purpose is to retrieve the hidden variable. The second function decorated by @pineapple_allowed.setter changes the hidden variable.
Getter and setter functions (=properties) can be useful if you want to perform additional calculation or validation on the internal variables.