Data Model

Callable Objects

__call__ lets an instance behave like a function while keeping state.

A callable object starts as ordinary state stored on an instance.

Source

class Multiplier:
    def __init__(self, factor):
        self.factor = factor
        self.calls = 0

double = Multiplier(2)
print(double.factor)

Output

__call__ makes the instance usable with function-call syntax.

Source

class Multiplier:
    def __init__(self, factor):
        self.factor = factor
        self.calls = 0

    def __call__(self, value):
        self.calls += 1
        return value * self.factor

double = Multiplier(2)
print(double(5))
print(double(7))

Output

10
14

Because the callable is still an object, it can remember state across calls.

Source

print(double.calls)

Output

Notes

callable(obj) checks whether an object can be called.
Callable objects are good for named, stateful behavior.
Prefer plain functions when no instance state is needed.

Run the complete example

Expected output

10
14
2

Execution time appears here after you run the example.

Callable Objects

See also

Run the complete example

Example code

Expected output