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

I've read What are Class methods in Python for? but the examples in that post are complex. I am looking for a clear, simple, bare-bones example of a particular use case for classmethods in Python.

Can you name a small, specific example use case where a Python classmethod would be the right tool for the job?

---

初始化的辅助方法：

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 instance

class 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.name
0
>>> y.name
Funky 1

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