Protected variable in Python

Prerequisites: Underscore ( _ ) in Python

A Variable is an identifier that we assign to a memory location which is used to hold values in a computer program. Variables are named locations of storage in the program. Based on access specification, variables can be public, protected and private in a class.

Protected variables are those data members of a class that can be accessed within the class and the classes derived from that class. In Python, there is no existence of “Public” instance variables. However, we use underscore ‘_’ symbol to determine the access control of a data member in a class. Any member prefixed with an underscore should be treated as a non-public part of the API or any Python code, whether it is a function, a method or a data member.

Example 1:

# program to illustrate protected
# data members in a class


# Defining a class
class Geek:

    # protected data members
    _name = "R2J"
    _roll = 1706256

    # public member function
    def displayNameAndRoll(self):

        # accessing protected data members
        print("Name: ", self._name)
        print("Roll: ", self._roll)


# creating objects of the class
obj = Geek()

# calling public member
# functions of the class
obj.displayNameAndRoll()

Output:

Name:  R2J
Roll:  1706256

Example 2: During Inheritance

# program to illustrate protected
# data members in a class


# super class
class Shape:

    # constructor
    def __init__(self, length, breadth):
        self._length = length
        self._breadth = breadth

    # public member function
    def displaySides(self):

        # accessing protected data members
        print("Length: ", self._length)
        print("Breadth: ", self._breadth)


# derived class
class Rectangle(Shape):

    # constructor
    def __init__(self, length, breadth):

        # Calling the constructor of
        # Super class
        Shape.__init__(self, length, breadth)

    # public member function
    def calculateArea(self):

        # accessing protected data members of super class
        print("Area: ", self._length * self._breadth)


# creating objects of the
# derived class
obj = Rectangle(80, 50)

# calling derived member
# functions of the class
obj.displaySides()

# calling public member
# functions of the class
obj.calculateArea()

Output:

Length:  80
Breadth:  50
Area:  4000

In the above example, the protected variables _length and _breadth of the super class Shape are accessed within the class by a member function displaySides() and can be accessed from class Rectangle which is derived from the Shape class. The member function calculateArea() of class Rectangle accesses the protected data members _length and _breadth of the super class Shape to calculate the area of the rectangle.