Python Property

Property is one of the most important concepts in python. Its performs the same operation of getter and setter in other programing languages

Normal function

Below program is a simple one which is not validating the age of the voter and allow them to add in voter list

class Voters:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def add_to_voter_list(self):
        print("Name: {} | Age: {} - Added to voters list successfully".format(self.name, self.age))

voter = Voters("John", 22)
voter.add_to_voter_list()

Output

Name: John | Age: 22 - Added to voters list successfully

Get and Set function

To overcome the problem in above program, we have implemented the get and set age functions and also validating the age is greater than 18

class Voters:
    def __init__(self, name, age):
        self.name = name
        self.set_age(age)

    def add_to_voter_list(self):
        print("Name: {} | Age: {} - Added to voters list successfully".format(self.name, self.age))

    #Getting the age
    def get_age(self):
        return self.age

    #Setting the age
    def set_age(self, age):
        if age>18:
            self.age = age
        else:
            raise ValueError("Age should be greater than 18")

voter1 = Voters("John", 28)
voter1.add_to_voter_list()

voter2 = Voters("David", 15)
voter2.add_to_voter_list()

Output

Name: John | Age: 28 - Added to voters list successfully
Traceback (most recent call last):
File "<string>", line 21, in <module>
File "<string>", line 4, in __init__
File "<string>", line 16, in set_age
ValueError: Age should be greater than 18

Issue in get and set method without property

But this program also have another issue, it is not allowing voter object to access its age attribute

class Voters:
    def __init__(self, name, age):
        self.name = name
        self.set_age(age)

    def add_to_voter_list(self):
        print("Name: {} | Age: {} - Added to voters list successfully".format(self.name, self._age))

    #Getting the age
    def get_age(self):
        return self._age

    #Setting the age
    def set_age(self, age):
        if age>18:
            self._age = age
        else:
            raise ValueError("Age should be greater than 18")

voter1 = Voters("John", 28)
voter1.add_to_voter_list()
print(voter1.name)
#It raises the error
print(voter1.age)

Output

Name: John | Age: 28 - Added to voters list successfully
John
Traceback (most recent call last):
File "<string>", line 23, in <module>
AttributeError: 'Voters' object has no attribute 'age'

Property class implementation

With the help of property class declaration for age, we can overcome the above issue and also validate the age value in our code like the below example program

class Voters:
    def __init__(self, name, age):
        self.name = name
        self.set_age(age)

    def add_to_voter_list(self):
        print("Name: {} | Age: {} - Added to voters list successfully".format(self.name, self._age))

    #Getting the age
    def get_age(self):
        return self._age

    #Setting the age
    def set_age(self, age):
        if age>18:
            self._age = age
        else:
            raise ValueError("Age should be greater than 18")

    #property declaration resolves the issue
    age = property(get_age, set_age)

voter1 = Voters("John", 28)
voter1.add_to_voter_list()
print(voter1.name)
print(voter1.age)

Output

Name: John | Age: 28 - Added to voters list successfully
John
28

Property Annotation

The same functionality can be achieved with the help of property annotations like the below example. Its pythonic way of implementing getter and setter functionality in our programs

class Voters: def init(self, name, age): self.name = name self.age = age

def add_to_voter_list(self):
    print("Name: {} | Age: {} - Added to voters list successfully".format(self.name, self.age))

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

@age.setter
def age(self, value):
    if value>18:
        self._age = value
    else:
        raise ValueError("Age should be greater than 18")

voter1 = Voters("John", 22)
voter1.add_to_voter_list()
print(voter1.name)
print(voter1.age)

Output

Name: John | Age: 22 - Added to voters list successfully
John
22