Can you explain what an object callable as a function, or a callable object, is?

A callable object in Python is an object that can be called like a function, meaning you can use parentheses with arguments: obj().

Objects are considered callable if they have a __call__ method defined.

Example:

class Multiplier:
    def __init__(self, factor):
        self.factor = factor
    def __call__(self, x):
        return x * self.factor

mul_by_3 = Multiplier(3)
print(mul_by_3(10))  # Outputs 30

Here, mul_by_3 is an object that behaves like a function, multiplying the input value by 3.

Callable objects are useful for creating objects with state that can be used as functions, for example, to configure call parameters.