Callable Objects

#python #programming #functions #datamodel

• We have different type of callable objects
  • built-in functions: len
  • classes: __init__
  • instances: using __call__
  • generator: with yield keyword
  • user defined functions with def and Lambda Function
• They are all called with ()
• How to know if object is callable: callable()
• How to type callable objects: Typing Callable
• Python Decorators is a type of callable object

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()

• Code above show an example of __call__
  • Good when you want to obtain the state of the object and preserve it state between calls
  • When you implement decorators

References

• Ramalho, 2022, p237-240