import numpy as np

y = np.array([4,7,9,1])
m1 = np.mean(y)  # Ok
m2 = y.mean()  # Ok
print(m1 == m2)  # True

x = [2,3]
r1 = np.concatenate([x, y]) # Ok
r2 = y.concatenate(x)  # AttributeError: 'numpy.ndarray' object has no attribute 'concatenate'
print(r1 == r2)

np.add(a,b)   <=> a+b   <=> a.__add__(b)
np.sin(a)    # no a.sin()