Getter and Setter in Python


In Python, getters and setters are not the same as those in other object-oriented programming languages. Basically, the main purpose of using getters and setters in object-oriented programs is to ensure data encapsulation. Private variables in python are not actually hidden fields like in other object oriented languages. Getters and Setters in python are often used when:

  • We use getters & setters to add validation logic around getting and setting a value.
  • To avoid direct access of a class field i.e. private variables cannot be accessed directly or modified by external user.

Using normal function to achieve getters and setters behaviour

To achieve getters & setters property, if we define normal get() and set() methods it will not reflect any special implementation. For Example

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# Python program showing a use
# of get() and set() method in
# normal function
  
class Geek:
    def __init__(self, age = 0):
         self._age = age
      
    # getter method
    def get_age(self):
        return self._age
      
    # setter method
    def set_age(self, x):
        self._age = x
  
raj = Geek()
  
# setting the age using setter
raj.set_age(21)
  
# retrieving age using getter
print(raj.get_age())
  
print(raj._age)

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Output:

21
21

In above code functions get_age() and set_age() acts as normal functions and doesn’t play any impact as getters and setters, to achieve such functionality Python has a special function property().



Using property() function to achieve getters and setters behaviour

In Python property()is a built-in function that creates and returns a property object. A property object has three methods, getter(), setter(), and delete(). property() function in Python has four arguments property(fget, fset, fdel, doc), fget is a function for retrieving an attribute value. fset is a fuction for setting an attribute value. fdel is a function for deleting an attribute value. doc creates a docstring for attribute. A property object has three methods, getter(), setter(), and delete() to specify fget, fset and fdel individually. For Example

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# Python program showing a
# use of property() function
  
class Geeks:
     def __init__(self):
          self._age = 0
       
     # function to get value of _age
     def get_age(self):
         print("getter method called")
         return self._age
       
     # function to set value of _age
     def set_age(self, a):
         print("setter method called")
         self._age = a
  
     # function to delete _age attribute
     def del_age(self):
         del self._age
     
     age = property(get_age, set_age, del_age) 
  
mark = Geeks()
  
mark.age = 10
  
print(mark.age)

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Output:

setter method called
getter method called
10

In above code there is only one print statement at line #25 but output consists of three lines due to setter method set_age() called in line #23 and getter method get_age() called in line #25. Hence age is a property object that helps to keep the access of private variable safe.

Using @property decorators to achieve getters and setters behaviour

In previous method we used property() function in order to achieve getters and setters behaviour. However as mentioned earlier in this post getters and setters are also used for validating the getting and setting of attributes value. There is one more way to implement property function i.e. by using decorator. Python @property is one of the built-in decorators. The main purpose of any decorator is to change your class methods or attributes in such a way so that the user of your class no need to make any change in their code. For Example

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# Python program showing the use of
# @property
  
class Geeks:
     def __init__(self):
          self._age = 0
       
     # using property decorator
     # a getter function
     @property
     def age(self):
         print("getter method called")
         return self._age
       
     # a setter function
     @age.setter
     def age(self, a):
         if(a < 18):
            raise ValueError("Sorry you age is below eligibility criteria")
         print("setter method called")
         self._age = a
  
mark = Geeks()
  
mark.age = 19
  
print(mark.age)

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Output:

setter method called
getter method called
19

In above code it is clear that how to use @property decorator to create getters & setters in pythonic way. Line 15-16 acts as a validation code that raises a ValueError if we try to initialize age with value less than 18, In this way any kind of validation can be applied in getter or setter functions .



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