Now that it's clear what a metaclass is, there is an associated concept that I use all the time without knowing what it really means.
I suppose everybody made once a mistake with parenthesis, resulting in an "object is not callable" exception. What's more, using __init__ and __new__ lead to wonder what this bloody __call__ can be used for.
Could you give me some explanations, including examples with the magic method ?
Answer
A callable is anything that can be called.
The built-in callable (PyCallable_Check in objects.c) checks if the argument is either:
- an instance of a class with a
__call__method or - is of a type that has a non null tp_call (c struct) member which indicates callability otherwise (such as in functions, methods etc.)
The method named __call__ is (according to the documentation)
Called when the instance is ''called'' as a function
Example
class Foo:
def __call__(self):
print 'called'
foo_instance = Foo()
foo_instance() #this is calling the __call__ method