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Python setattr() Function

The setattr() method returns the value of the named attribute of an object. If not found, it returns the default value provided to the function.

Syntax​

setattr(object, name, value)

setattr() Parameters​

Python setattr() function parameters:

ParameterConditionDescription
objectRequiredObject whose attribute has to be set
nameRequiredString that contains the attribute's name
valueRequiredValue given to the attribute

setattr() Return Value​

Python setattr() function returns None.

Examples​

Example 1: Basic usage of setattr() function to add a new Attribute​

For example, consider the Person class defined with an attribute name. Create an instance p of Person and then use setattr() to add a new attribute age with value 25.

class Person:
    def __init__(self, name):
        self.name = name

p = Person('Tom')
setattr(p, 'age',  25)

print(p.name) # Output: Tom
print(p.age)  # Output: 25

output

Tom
25
note

You can add a new attribute and assign a value to it only if the object implements the __dict__() method.

You can check if your class implement __dict__() by using the dir() function in this way:

class Person:
    def __init__(self, name):
        self.name = name

print(dir(Person))

output

['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']

Example 2: Modifying an Existing Attribute​

setattr() function can be used to modify an existing attribute of an object.

In the following example, the Person instance p has a name attribute set to 'Tom'. setattr() function is then used to change the name attribute to 'Ryan'.

The output shows that the name attribute has been successfully modified.

class Person:
    name = 'Tom'

p = Person()
print('Before modification:', p.name)

# Setting name to 'Ryan'
setattr(p, 'name', 'Ryan')

print('After modification:', p.name)  # Output: Ryan

output

Before modification: Tom
After modification: Ryan

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