python numpy.array axis

import numpy as np
ls = np.array([[1, 2], [3, 4]])

均值：

print(np.mean(ls))

每一列的均值：

print(np.mean(ls, axis = 0))

([2, 3])

每一行的均值：

print(np.mean(ls, axis = 1))

([1.5, 3.5])