Python: getattr() function

getattr() overview
The getattr() function returns the value of the given attribute of an object. If the attribute is not found, it returns the default value. If no default value is provided, an AttributeError exception is raised.

getattr() for existing attributes
If the attribute exists in the object, it is returned by the getattr() function.


# getattr() for exisiting attributes
class Dog:
   age = 4
   name = "Mike"

myDog = Dog()
print('The age of ', getattr(myDog, "name"), ' is ', getattr(myDog, "age"))


The attributes are returned and printed.

The age of  Mike  is  4

getattr() with default value
If the attribute does not exists in the object and a default value is provided in the getattr() function, the default value is returned.


# getattr() with default values
class Dog:
   age = 4
   name = "Mike"

myDog = Dog()
print('The age of ', getattr(myDog, "name"), ' is ', getattr(myDog, "age"), ' and the breed is ', getattr(myDog, "breed", "husky"))


The breed attribute is not existent, the default value is returned and printed.

The age of  Mike  is  4  and the breed is  husky

getattr() when attribute does not exist
If the attribute does not exists and a default value is not defined, a AttributeError exception is raised.


# getattr() when attribute does not exist and default value is not set
class Dog:
   name = "Mike"

myDog = Dog()
print('The age of ', getattr(myDog, "name"), ' is ', getattr(myDog, "age"))


The attribute age is missing and a default value is not set, a AttributeError exception is raised.

AttributeError: 'Dog' object has no attribute 'age'

getattr() syntax
The syntax of the getattr() function is:

getattr(object, attribute_name[, default_value])

getattr() arguments
The getattr() function accepts two or three arguments. The first two arguments are required, while the third argument is optional.


required: object, the object to be checked
required: attribute_name, the name of the attribute as string
optional: default_value, the default_value to be returned if the attribute is not found


getattr() return value
The getattr() function returns the attribute value if the attribute is found. If the attribute is not found, it returns the default value. If the default value is not specified a AttributeError exception is raised.

related functions
The related functions of the getattr() function are the hasattr() function to check if an attribute exists and the delattr() function to delete an existing attribute. The dir() function can be used to list all valid attributes of an given object.