human
I wrote the below code

    old_precondition = cls.check_precondition
    def check_precondition():
        (result, message) = fn()
        if (not result):
            return (result, message)
        return old_precondition()
    return staticmethod(check_precondition)

What's a good function header?
 Here's a good function header?
assistant
#Here's a good function header.

def _build_precondition_join_fn(cls, fn):