We looked at three of the special methods for class definition. The __call__() method is used when creating a callable. The callable is used to create functions that are stateful. Our primary example is a function that memoizes previous results.

The __enter__() and __exit__() methods are used to create a context manager. The context is used to handle processing that is localized to the body of a with statement. Most of our examples include input-output processing. Python also uses localized contexts for the decimal state. Other examples include making patches for unit testing purposes or acquiring and releasing locks.