Question

For example, I need for class calling returns string.

class Foo(object):
    def __init__(self):
        self.bar = 'bar'

    def __call__(self):
        return self.bar

Foo calling returns Foo object.

Foo()
<__main__.Foo object at 0x8ff6a8c>

What should I do to class returns string or other? How to use __call__?

Answer 1

With your example (of limited usefulness), you have a class of callable objects.

You can do now, as you have done,

>>> o = Foo()
>>> o
<__main__.Foo object at 0x8ff6a8c>
>>> o()
'bar'

I. e., __call__() does not make your class callable (as it is already), but it gives you a callable object.