@property.setter

Let's go back to the User class with a private attribute password that cannot be changed in subclasses. How can we access the private password? Let's create a property that returns the private password:


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class User:
    def __init__(self, username, password):
        self.username = username
        self.__password = password

    @property
    def password(self):
        return self.__password

bob = User("bob123top", "bob123456")
print(bob.password)

Currently, we can retrieve the password but cannot change it using the regular syntax. To be able to set a value for a property, we need to use the @{property name}.setter decorator, where {property name} is the name of the property we have created (the one for which we want to set a setter).


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class User:
    def __init__(self, username, password):
        self.username = username
        self.__password = password

    @property
    def password(self):
        return self.__password

    @password.setter
    def password(self, new_password):
        self.__password = new_password


bob = User("bob123top", "bob123456")
print("(old)", bob.password)

bob.password = "new_bob_password_123"
print("(new)", bob.password)

The @password.setter decorator indicates that this method should be invoked whenever the password property is assigned a new value. The second password method is decorated by @password.setter (where password is the name of the property method) and set up a new password via assignment (=) operation. The password setter method takes two parameters: self (referring to the instance of the class) and new_password (representing the new value being assigned to the password attribute).

Let's choose the following password restrictions:

The password must be of a type string.
Password length must be greater than 8.

If the new password does not meet the requirements, the corresponding messages will be printed.


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class User:
    def __init__(self, username, password):
        self.username = username
        self.__password = password

    @property
    def password(self):
        return self.__password

    @password.setter
    def password(self, new_password):
        if isinstance(new_password, str):
            if len(new_password) >= 8:
                self.__password = new_password
            else:
                print("The password length must be >= 8")
        else:
            print("Password must be STRING")



bob = User("bob123top", "bob123456")
print("(old)", bob.password)

bob.password = 122
print("(old)", bob.password)

bob.password = "123"
print("(old)", bob.password)

bob.password = "bob.top.user.123"
print("(new)", bob.password)

This code ensures that whenever a new value is assigned to the password attribute, it undergoes validation checks for length and type, providing appropriate feedback if the new password does not meet the requirements.

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