CH8 np.diff uses n as if it is the number of periods to difference, but it actually differences n times.

[jcurtiswebb]

This issue occurs both in the chapter and in the exercises. n is used to attempt to create a seasonal difference, but it is actually differencing the time series n times.

From the numpy documentation:

parameter n int, optional
The number of times values are differenced. If zero, the input is returned as-is.