How to define a __str__ method for a class?

Question

In Python, the object class serves as the root superclass for all the (new-style) classes. By default at least, applying str and repr to the "class instance" of any subclass of object produces the same result:

>>> class spam(object): pass ...  >>> str(spam) "<class '__main__.spam'>" >>> str(spam) == repr(spam) 

I would like to define a subclass of object, say fancyobject, that is identical to object in every way, except that applying str and repr to fancyobject itself produces different outputs:

>>> class ham(fancyobject): pass ... >>> str(ham) 'ham' >>> repr(ham) "<class '__main__.ham'>" 

Is there a way to do this in Python?

PS: I'm aware of the __str__ special method, but it is my understanding that if class A overrides __str__, then the overriding method is called only when str is called on instances of A, not when it is called on A itself. I.e.:

>>> class A(object): ...     def __str__(self): ...         return 'from new __str__: ' + object.__str__(self) ...  >>> str(A()) 'from new __str__: <__main__.A object at 0x7f79c62a5310>' >>> str(A) "<class '__main__.A'>" 

Answer 1

Actually the same mechanism as for object instances applies for types. Types are just objects themselves, so they are converted to strings by calling the __str__() method on their type, which is called the "metaclass". So you have to overwrite the __str__() method on the metaclass:

class fancytype(type):     def __str__(self):         return self.__name__ class ham(object):     __metaclass__ = fancytype print ham 

prints

ham 

Answer 2

You can also set the default metaclass for a whole module like this

class fancytype(type):     def __str__(self):         return self.__name__  __metaclass__ = fancytype  class ham:     pass print ham