when you want to use both a classmethod and the function with a class instance

classinstancemethod

# classinstancemethod, when you want to use both a classmethod and the function with a class instance

## Descriptors

## Anything with __get__ and optionally __set__:

class classinstancemethod(object):
    def __init__(self, func):
        self.func = func
    def __get__(self, obj, type=None):
        def repl(*args, **kw):
            return self.func(obj, type, *args, **kw)
        return repl


## Then to use it:

class MyValidator(object):
    date_format = '%Y-%m-%d'

    def __init__(self, date_format=None):
        if date_format is not None:
            self.date_format = date_format

    @classinstancemethod
    def check_input(self, cls, input):
        if self is None:
            self = cls()
        return time.strptime(input, self.date_format)

MyValidator('%m-%d-%Y').check_input('5-1-2010')
MyValidator.check_input('2010-05-01')