Python __set_name__() Magic Method
Python’s magic method obj.__set_name__(self, owner, name) method is created on an attribute obj when the class owner holding the attribute is created.
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.__set_name__(self, owner, name)class Attribute: pass class My_Class: x = Attribute() # Python calls: x.__set_name__(My_Class, 'x')
The expression x = Attribute() internally causes Python to call x.__set_name__(My_Class, ‘x’) .
Overriding __set_name__() Example
Let’s override the __set_name__ magic method on the Attribute ‘s class:
class Attribute: def __set_name__(self, owner, name): print('Python is great!') class My_Class: x = Attribute() In fact, the magic method is called which results in the output:
More Practical Example
The purpose of the magic method __set_name__() , however, is not to print dummy strings to the Python shell—as you may have guessed already.
💡 Note: The __set_name__() method is called automatically by Python for every single attribute held by the owner class object when initializing an object—in our previous example an object of type My_Class . More details here.
However, the __set_name__() method is not called when assigning attributes to an object dynamically—later in the code.
To see what I mean, have a look at this code snippet:
class Attribute: def __set_name__(self, owner, name): print(‘Python is great!’) class My_Class: pass My_Class.x = Attribute() # x.__set_name__() is NOT called!! #
Now, you can manually call the __set_name__() method to run the same routine you’d have run if you’d initialized the attribute in the class definition right away:
class Attribute: def __set_name__(self, owner, name): print('Python is great!') class My_Class: pass My_Class.x = Attribute() # My_Class.x.__set_name__(My_Class, 'x') # Python is great! Where to Go From Here?
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