Numpy axis /Numpy.ufunc.identity

轴用来为超过一维的数组定义的属性，二维数据拥有两个轴：第0轴沿着行的垂直往下，第1轴沿着列的方向水平延伸

https://www.cnblogs.com/rrttp/p/8028421.html

2.

for the ufunc np.add, ufct.identity is 0. But for another function it may be something else. For instance, np.multiply.identity is 1.

The ufunc_reduce function you show doesn't know in advance what function it will be given, so it can't be hard-coded to use either 0 or 1. It gets the proper value by checking the identity attribute of the ufunc instead.

https://stackoverflow.com/questions/41906867/usage-of-numpy-ufunc-identity