The line should be:
numpy.concatenate([a,b])
The arrays you want to concatenate need to be passed in as a sequence, not as separate arguments.
From the NumPy documentation:
numpy.concatenate((a1, a2, ...), axis=0)
Join a sequence of arrays together.
It was trying to interpret your b
as the axis parameter, which is why it complained it couldn’t convert it into a scalar.