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How does __repr__ help with debugging when printing a list of custom objects? How do you overload arithmetic operators like + and - using __add__ and __sub__? What do __eq__ and __hash__ need to satisfy together, and what happens if you only override __eq__? How do __len__, __getitem__, and __setitem__ let a custom class act like a sequence or mapping? How do comparison magic methods like __lt__, __le__, __gt__, and __ge__ support custom sorting? How does __contains__ let you customize the behavior of the 'in' operator? How do you implement custom attribute access with __getattr__ versus __getattribute__? How do context manager magic methods __enter__ and __exit__ work, and what does __exit__'s return value control? What is the difference between __new__ and __init__, and when would you override __new__? How do __iadd__ and other in-place operator methods (__isub__, __imul__) differ from their non-in-place counterparts?
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Python › Magic Methods & Operator Overloading

How does __call__ let an instance of a class be invoked like a function?

Intermediate

Answer

Defining __call__(self, *args, **kwargs) makes instances callable with parentheses, e.g., obj(x, y), which Python translates to obj.__call__(x, y). This is used for stateful callables like decorators-as-classes, memoized functions, or configurable strategy objects that need to remember state between calls.
class Multiplier:
    def __init__(self, factor):
        self.factor = factor
    def __call__(self, x):
        return x * self.factor

double = Multiplier(2)
print(double(5))  # 10 -- called like a function
Real-world example A machine learning preprocessing pipeline defines transform classes with __call__ so each transform can be applied like a function while still holding configuration state (e.g., normalization parameters).

Common follow-ups: How does __call__ enable class-based decorators?;What's the performance difference vs a plain function?

Decorators;Descriptors & Properties
All 15 Magic Methods & Operator Overloading questions