取ndarray的某几个数，若写为：

a = np.array([0,1,2,3,4,5,6])
index = np.array([1,2,3])
b = a(index)
print(b)

则会报错TypeError: 'numpy.ndarray' object is not callable

正确写法为：

a = np.array([0,1,2,3,4,5,6])
index = np.array([1,2,3])
b = a[index]
print(b)