What's an example use case for a Python classmethod?

Helper methods for initialization:

class MyStream(object):    @classmethod    def from_file(cls, filepath, ignore_comments=False):            with open(filepath, 'r') as fileobj:            for obj in cls(fileobj, ignore_comments):                yield obj    @classmethod    def from_socket(cls, socket, ignore_comments=False):        raise NotImplemented # Placeholder until implemented    def __init__(self, iterable, ignore_comments=False):       ...

Well __new__ is a pretty important classmethod. It's where instances usually come from

so dict() calls dict.__new__ of course, but there is another handy way to make dicts sometimes which is the classmethod dict.fromkeys()

eg.

>>> dict.fromkeys("12345"){'1': None, '3': None, '2': None, '5': None, '4': None}

I don't know, something like named constructor methods?

class UniqueIdentifier(object):    value = 0    def __init__(self, name):        self.name = name    @classmethod    def produce(cls):        instance = cls(cls.value)        cls.value += 1        return instanceclass FunkyUniqueIdentifier(UniqueIdentifier):    @classmethod    def produce(cls):        instance = super(FunkyUniqueIdentifier, cls).produce()        instance.name = "Funky %s" % instance.name        return instance

Usage:

>>> x = UniqueIdentifier.produce()>>> y = FunkyUniqueIdentifier.produce()>>> x.name0>>> y.nameFunky 1