Concatenating two one-dimensional NumPy arrays

How do I concatenate two one-dimensional arrays in NumPy? I tried numpy.concatenate:

import numpy as np
a = np.array([1, 2, 3])
b = np.array([4, 5])
np.concatenate(a, b)

But I get an error:

TypeError: only length-1 arrays can be converted to Python scalars