Python’s magic method
__getattr__() implements the built-in
getattr() function that returns the value associated with a given attribute name. Additionally,
__getattr__() is called if the normal attribute access (e.g.,
my_object.my_attribute) results in an
We call this a “Dunder Method” for “Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.
Syntax and Example
Let’s have a look at an example where you override the
__getattr__ magic method of a custom class
Person to simply print out the string
'hello world' when calling the
getattr() built-in function.
class Person: def __getattr__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world
__getattr__() is also called if you try to access an attribute that doesn’t exist and, thus, would yield an
class Person: def __getattr__(self, attr_name): print('hello world') alice = Person() alice.age # attribute doesn't exist! # hello world
Here’s what would’ve happened in the same scenario without defining the
__getattr__() magic method:
class Person: pass alice = Person() alice.age # attribute doesn't exist!
alice.age attribute doesn’t exist, Python raises an
Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 6, in <module> alice.age # attribute doesn't exist! AttributeError: 'Person' object has no attribute 'age'
You can see this scenario next in our recap on the built-in
getattr(object, string) function returns the value of the
object‘s attribute with name
If this doesn’t exist, it returns the value provided as an optional third
If that doesn’t exist either, it raises an
An example is
getattr(porsche, 'speed') which is equivalent to
# Define class with one attribute class Car: def __init__(self, brand, speed): self.brand = brand self.speed = speed # Create object porsche = Car('porsche', 100) tesla = Car('tesla', 110) # Two alternatives to get instance attributes: print(getattr(porsche, 'brand') + " " + str(getattr(porsche, 'speed'))) print(tesla.brand + " " + str(tesla.speed)) # Get an attribute that doesn't exist with default argument: print(getattr(porsche, 'color', 'red'))
porsche 100 tesla 110 red
Where to Go From Here?
Enough theory. Let’s get some practice!
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.