__setattr__ — Easy Examples

Called on every attribute assignment

EasyIntermediateAdvancedExpert

Implementing __setattr__

Basic implementation of __setattr__ in a class.

python
class Example:
    def __setattr__(self):
        return "Example __setattr__"

obj = Example()
print(obj)

__setattr__ called on every attribute assignment. Implementing it lets you customize how Python interacts with your objects.

__setattr__ in action

Seeing __setattr__ called by Python's built-in operations.

python
# How Python calls __setattr__ automatically
class Demo:
    def __init__(self, value):
        self.value = value

    def __setattr__(self):
        print(f"__setattr__ was called!")
        return self

d = Demo(42)
# This triggers __setattr__:
print(d)

Python automatically calls __setattr__ when you use the corresponding operator or function on your object.

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