newbie question, when __call__ method is used?

[chenyu]

Hi everyone,
I have read other's code, and found it contains the __call__. But I
don't know when its code will be executed.
>From the Python manual, I know it is built-in function and is a
callback function. But the manual doesn't contain any simple example.

Could you give me an simple example to explain when its code will be
executed?



Thank you for your attention.
kind regards/chenyu