Python’s magic method __getattribute__() implements the built-in getattr() function that returns the value associated with a given attribute name. If the __getattribute__() error results in an class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 0 due to a non-existent attribute, Python will call the class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 1 function for resolution.
Thus, the __getattribute__() method takes precedence over the class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 1 method.
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 Minimal Example
object.__getattribute__(self, attr_name)Let’s have a look at an example where you override the class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 4 magic method of a custom class class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 5 to simply print out the string class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 6 when calling the getattr() built-in function.
class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world__getattribute__ vs __getattr__
The class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 4 method is similar to class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 9. What’s the difference?
Assume a user wants to access an attribute from a given object like so:
my_obj.my_attr- my_obj.my_attr0 is called first. If it yields an class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 0, Python will hand it to:
- my_obj.my_attr2 which is called second.
You can see that the former takes precedence over the latter in the following code snippet that defines both methods—but __getattribute__() is taken as it doesn’t result in an error.
class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello worldHere’s what would’ve happened in the same scenario when raising an class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 0 in class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 4:
class Person: def __getattribute__(self, attr_name): raise AttributeError def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello universePython doesn’t even mention the error but passes the execution flow to the class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 1 method.
Background getattr()
Python’s built-in my_obj.my_attr7 function returns the value of the my_obj.my_attr8‘s attribute with name my_obj.my_attr9.
If this doesn’t exist, it returns the value provided as an optional third class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 0 argument.
If that doesn’t exist either, it raises an class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 0.
Python getattr() - Ultimate Guide
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An example is class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 2 which is equivalent to class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 3.
# 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'))Output:
porsche 100 tesla 110 redFurther Reading:
- Python class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 4 magic method
- Python class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 5 built-in function
- Python class Person: def __getattribute__(self, attr_name): print('hello world') def __getattr__(self, attr_name): print('hello universe') alice = Person() getattr(alice, 'age') # hello world 6 built-in function
- Python class Person: def __getattribute__(self, attr_name): print('hello world') alice = Person() getattr(alice, 'age') # hello world 1 vs __getattribute__()
- //docs.python.org/3/reference/datamodel.html
Where to Go From Here?
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Chris
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. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
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