Question

How do I override a class special method?

I want to be able to call the __str__() method of the class without creating an instance. Example:

class Foo:
    def __str__(self):
        return 'Bar'

class StaticFoo:
    @staticmethod
    def __str__():
        return 'StaticBar'

class ClassFoo:
    @classmethod
    def __str__(cls):
        return 'ClassBar'

if __name__ == '__main__':
    print(Foo)
    print(Foo())
    print(StaticFoo)
    print(StaticFoo())
    print(ClassFoo)
    print(ClassFoo())

produces:

<class '__main__.Foo'>
Bar
<class '__main__.StaticFoo'>
StaticBar
<class '__main__.ClassFoo'>
ClassBar

should be:

Bar
Bar
StaticBar
StaticBar
ClassBar
ClassBar

Even if I use the @staticmethod or @classmethod the __str__ is still using the built-in Python definition for __str__. It’s only working when it’s Foo().__str__() instead of Foo.__str__().

Answer 1

Special method __str__ defined in a class works only for the instances of that class, to have the different behavior for class objects you will have to do it in a metaclass of that class e.g. (python 2.5)

class Meta(type):
    def __str__(self):
        return "Klass"

class A(object):
    __metaclass__ = Meta

    def __str__(self):
        return "instance"

print A
print A()

output:

Klass
instance