Python isinstance（）浮动失败的断言测试

Background:
I've been completing a course in machine learning and neural networks, and in the following where I experienced a problem, we're required to compute the cost function. There are two ways to do so by applying a np.multiply and np.sum OR by np.dot. I've called these cost1 and cost2, respectively in the example. They produce the same result. I've been completing a course in ma