Using Python's setattr(), hasattr(), and getattr() Functions

The setattr() function sets the value of an existing attribute on an object. Its syntax is setattr(object, name, value) , where object is the target, name is the attribute name as a string, and value is the new value. It returns nothing.

Example:

class A(object):
    bar = 1

a = A()
print(1, getattr(a, 'bar'))  # get attribute 'bar'
# >>> 1
setattr(a, 'bar', 5)          # set attribute 'bar' to 5
print(a.bar)
# >>> 5

The hasattr() function checks whether an object possesses a given attribute, returning True or False . Syntax: hasattr(object, name) .

Example:

#!/usr/bin/python
# -*- coding: UTF-8 -*-
class Coordinate:
    x = 10
    y = -5
    z = 0

point1 = Coordinate()
print(hasattr(point1, 'x'))   # True
print(hasattr(point1, 'y'))   # True
print(hasattr(point1, 'z'))   # True
print(hasattr(point1, 'no'))  # False

The getattr() function retrieves the value of an attribute, optionally providing a default if the attribute does not exist. Syntax: getattr(object, name[, default]) . If the attribute is missing and no default is supplied, an AttributeError is raised.

Example:

class A(object):
    bar = 1

a = A()
print(getattr(a, 'bar'))          # >>> 1
print(getattr(a, 'bar2'))         # raises AttributeError
print(getattr(a, 'bar2', 3))      # >>> 3 (default value)

Additional notes: setattr() can also create a new attribute if it does not already exist. hasattr() requires the attribute name as a string, and getattr() can be used to obtain methods, returning the method object or its memory address.