JuniorTheoryCommon

What does this program print?

Python

import numpy as np

X = np.ones((4, 3))
m = X.mean(axis=0)
print(m.shape, (X - m).shape)

(3,) (4, 3)

Expecting (4,): axis=0 collapses the rows, leaving one mean per column, so m has 3 values.
Expecting a ValueError for subtracting a (3,) array from a (4, 3) one: broadcasting matches the last axis and repeats m for every row.