What is the correct way of structuring private methods that are going to be called inside a classmethod?

What is the correct way of structuring private methods that are going to be called inside a classmethod? There is such a thing as a private classmethod?

class Foo:
    def _bar(self):
        # do something

    @classmethod
    def bar(cls):
        cls._bar()


>> Foo.bar()

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 7, in bar
TypeError: unbound method _bar() must be called with Foo instance as first argument (got nothing instead)