Python setattr() method

Python setattr() method is used to assign the object attribute its value. The setattr() can also be used to initialize a new object attribute. Also, setattr() can be used to assign None to any object attribute.

Example :

class Person:
    def __init__(self):
        pass

p = Person()
setattr(p, 'name', 'kiran')
print(f"name: {p.name}")

Output :

name: kiran

Python setattr() Function Syntax

Syntax : setattr(obj, var, val)

Parameters : 

• obj : Object whose which attribute is to be assigned.
• var : object attribute which has to be assigned.
• val : value with which variable is to be assigned.

Returns : None

Python setattr() Examples

How setattr() works in Python?

In the given example, we have defined a animal class with a class variable name and we are showing how can we set the value of the variable with setattr().

class Animal:
    name = 'lucky'
    
p = Animal()
print('Before modification:', p.name)
setattr(p, 'name', 'Woozoo')

print('After modification:', p.name)

Output :

Before modification: lucky
After modification: Woozoo

When the attribute is not found in setattr() in Python

In this example, we have defined a Gfg class and we have set the name and descr variables to None after that we have set the variable with setattr() and printed it. After that, we created a variable named a value that was not found in the class with setattr() and printing it in Python.

class Gfg:
    name = None
    descr = None


# initializing object
gfg = Gfg()

print("Before using setattr:\n"
      f"\tname: {gfg.name}\n"
      f"\tdescr: {gfg.descr}")

# setting value using setattr
setattr(gfg, "name", "GeeksForGeeks")
setattr(gfg, "descr", "CS Portal")

print("After using setattr:\n"
      f"\tname: {gfg.name}\n"
      f"\tdescr: {gfg.descr}")

# creating new attribute using setattr
setattr(gfg, 'value', 5)
print(f"\nNew attribute created, gfg.value: {gfg.value}")

Output : 

Before using setattr:
    name: None
    descr: None
After using setattr:
    name: GeeksForGeeks
    descr: CS Portal

New attribute created, gfg.value: 5

Python setattr() dict

Here we are creating attributes of the class 'Dict2Class' dynamically using setattr() function by passing a dictionary with some keys and values to the __init__() method of the class.

class Dict2Class(object):
    def __init__(self, my_dict):
        for key in my_dict:
            setattr(self, key, my_dict[key])

# Driver Code
if __name__ == "__main__":
    
    # Creating the dictionary
    my_dict = {"Name": "Geeks",
            "Rank": "1223",
            "Subject": "Python"}
    
    result = Dict2Class(my_dict)
    
    # printing the result
    print("After Converting Dictionary to Class : ")
    print(result.Name, result.Rank, result.Subject)
    print(type(result))

Output :

After Converting Dictionary to Class : 
Geeks 1223 Python
<class '__main__.Dict2Class'>

Python setattr() exception

Here we will create read-only attributes of the object using property() function in Python and if we try to set the attribute's value using setattr() function then an exception will rise.

class Person:

    def __init__(self):
        self._name = None

    def name(self):
        print('name function called')
        return self._name

    # for read-only attribute
    n = property(name, None)

p = Person()

setattr(p, 'n', 'rajav')

Output :

---> 16 setattr(p, 'n', 'rajav')
AttributeError: can't set attribute