python 用元类检查做约束

def __init__(self, clsname, bases, clsdict):
    super().__init__(clsname, bases, clsdict)
    sup = super(self, self)
    for name, value in clsdict.items():
        if name.startswith('_') or not callable(value):
            continue
        # Get the previous definition (if any) and compare the signatures
        prev_dfn = getattr(sup,name,None)
        if prev_dfn:
            prev_sig = signature(prev_dfn)
            val_sig = signature(value)
            if prev_sig != val_sig:
                logging.warning('Signature mismatch in %s. %s != %s',
                                value.__qualname__, prev_sig, val_sig)

def spam(self, x, *, z):
    pass

def spam(self,x,z):
    pass