请简单解释Python中 staticmethod(静态方法)和 classmethod(类方法), 并分别补充代码执行下列方法。 class A (object) : def foo (self, x) : print( "executing foo(%s, %s)" % (self,x)) @classmethod def class_foo (cls, x) : print( "executing class_foo(%s, %s)" % (cls,x)) @staticmethod def static_foo (x) : print( "executing static_foo(%s)" % (x)) a = A()