python中的欧拉-罗德里格斯公式不返回期望的旋转值

I have a function that produces a rotation matrix according to the Euler-Rodrigues formula in python. However when I rotate an array by half pi it does not sit 90 degrees to the original vector and I am not sure why. If I rotate by pi or 2pi then I get the expected rotation. The code is as follows.I have a function that produces a rotation matr