import numpy as np

morning = np.array([18, 21, 24])
evening = np.array([15, 19, 23])

by_reading = np.stack((morning, evening), axis=0)
by_city = np.stack((morning, evening), axis=-1)

print("axis=0:")
print(by_reading)
print("axis=0 shape:", by_reading.shape)
print("axis=-1:")
print(by_city)
print("axis=-1 shape:", by_city.shape)