setattr()

setattr(object, name, value)

Returns: None · Updated March 13, 2026 · Built-in Functions

built-in attributes objects

The setattr() function sets an attribute on an object using its name as a string. It provides runtime attribute assignment, which is useful when the attribute name is not known until the code executes.

Syntax

setattr(object, name, value)

Parameters

Parameter	Type	Default	Description
`object`	object	—	Any object that supports attribute assignment
`name`	`str`	—	The attribute name as a string
`value`	any	—	The value to assign to the attribute

Examples

Basic usage

class Person:
    pass

person = Person()
setattr(person, "name", "Alice")
setattr(person, "age", 30)

print(person.name)
# Alice
print(person.age)
# 30

Dynamic attribute assignment

class Config:
    pass

config = Config()
settings = {"host": "localhost", "port": 8080, "debug": True}

for key, value in settings.items():
    setattr(config, key, value)

print(config.host)
# localhost
print(config.debug)
# True

Setting attributes on existing objects

import math

setattr(math, "MY_CONSTANT", 42)
print(math.MY_CONSTANT)
# 42

Common Patterns

Building objects dynamically

def create_object(cls_name, **attrs):
    cls = type(cls_name, (), {})
    obj = cls()
    for key, value in attrs.items():
        setattr(obj, key, value)
    return obj

user = create_object("User", name="Bob", email="bob@example.com")
print(user.name)
# Bob

Combining with getattr

class Robot:
    def __init__(self):
        self.x = 0
        self.y = 0

robot = Robot()
setattr(robot, "direction", "north")

direction = getattr(robot, "direction", "unknown")
print(direction)
# north

Errors

AttributeError: Raised when the object does not allow attribute assignment (e.g., frozen objects)
TypeError: Raised when name is not a string