python - numpy.round 的奇怪行为

Question

Python 的 round() 似乎总是在遇到 x.5 数字时四舍五入:

print round(1.5),round(2.5),round(3.5),round(4.5)
>>> 2.0 3.0 4.0 5.0

但是numpy.round()似乎不一致:

import numpy as np
print np.round(1.5),np.round(2.5),np.round(3.5),np.round(4.5)
>>> 2.0 2.0 4.0 4.0

这在某些情况下可能会引入错误。这是错误还是我遗漏了什么？

Answer 1

numpy 舍入到最接近的偶数:

https://docs.scipy.org/doc/numpy/reference/generated/numpy.around.html#numpy.around

For values exactly halfway between rounded decimal values, NumPy rounds to the nearest even value. Thus 1.5 and 2.5 round to 2.0, -0.5 and 0.5 round to 0.0, etc.