+++ slug = "callable-objects" title = "Callable Objects" section = "Data Model" summary = "call lets an instance behave like a function while keeping state." doc_path = "/reference/datamodel.html#object.call" see_also = [ "functions", "closures", "callable-types", "bound-and-unbound-methods", ] +++

Functions are not the only callable objects in Python. Any instance can be called with parentheses when its class defines __call__.

Callable objects are useful when behavior needs remembered configuration or evolving state. A closure can do this too; a class is often clearer when the state has multiple fields or needs named methods.

The tradeoff is ceremony. Use a function for simple behavior, a closure for small captured state, and a callable object when naming the state improves the interface.

:::program

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))
print(double.calls)

:::

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

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

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

2

:::

:::cell __call__ makes the instance usable with function-call syntax.

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))

10
14

:::

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

print(double.calls)

2

:::

:::note

• 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. :::