Read Only Properties in Python

Last Updated : 10 Jul, 2020

Prerequisites: Python Classes and Objects

A class is a user-defined blueprint or prototype from which objects are created. Classes provide a means of bundling data and functionality together. Creating a new class creates a new type of object, allowing new instances of that type to be made. To put it in simple words, let us assume a class Student, a student can have many properties such as Name, Course, Student’s ID, etc. Now let us assume we have a Student named Anita pursuing MBA, Anita is an object of class Student.

Example:

class student: 
      
    def __init__(self, name, course): 
        self.name = name 
        self.course = course 
  
    def studentid(self): 
        return "student's identification number is \ 
        {}{}".format(self.name, self.course) 
  
student1 = student("Anita", "MBA") 
print(student1.studentid()) 

Output:

student's identification number is AnitaMBA

Now, We want to access student id as a property and not as a method. For this all required is to add @property decorator before the method.

Example:

class student: 
      
    def __init__(self, name, course): 
        self.name = name 
        self.course = course 
  
    @property
    def studentid(self): 
        return "student's identification number is \ 
        {}{}".format(self.name, self.course) 
  
student1 = student("Anita", "MBA") 
print(student1.studentid) 

Output:

student's identification number is AnitaMBA

A Read-Only-Property is a property decorator without a setter. The student id here is a read-only-property since it doesn’t have a setter. In general terms, it means that the value is not changeable. To understand let’s take one more example:

Example:

class employee: 
    def __init__(self, basesalary, yearsofworking): 
        self.basesalary = basesalary 
        self.yearsofworking = yearsofworking 
      
    @property
    def salary(self): 
        self.salary = 50000
  
amit = employee(20000, 5) 
amit.salary = 10000
print(amit.basesalary, amit.yearsworking, amit.salary) 

Output:

Traceback (most recent call last):
File “/home/e029e0b9ccad85905e22dd5a91943897.py”, line 14, in
amit.salary = 10000
AttributeError: can’t set attribute

To fix this one setter is to be added in this code. After doing this, it will no longer be a read-only-property.

Example:

class employee: 
    def __init__(self, basesalary, yearsofworking): 
        self.basesalary = basesalary 
        self.yearsofworking = yearsofworking 
        self._salary = 0
      
    @property
    def salary(self): 
        return self._salary 
  
    @salary.setter 
    def salary(self, salary): 
        self._salary = salary 
  
amit = employee(20000, 5) 
amit.salary = 10000
print(amit.basesalary, amit.yearsofworking, amit.salary) 

Output:

20000 5 10000

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course.

My Personal Notes

Related Articles