User-Defined Callable Types
In Python, we can make arbitrary objects behave like functions by implementing a __call__ instance method. This simple approach allows us to create function-like objects with internal state that persists across invocations. By defining the __call__ method, we enable instances of the class to be callable, just like regular functions.
user_callable_object.py
>>> import random
>>> class BingoCage:
>>> def __init__(self, items):
... self._items = list(items)
... random.shuffle(self._items)
>>> def pick(self):
... try:
... return self._items.pop()
... except IndexError:
... raise LookupError('pick from empty BingoCage')
>>> def __call__(self):
... return self.pick()
>>> bingo = BingoCage(range(3))
>>> print(bingo.pick())
>>> print(bingo())
>>> print(callable(bingo))
0
1
True