I think this line is more readable without the spaces after commas, but as I am not particularly bothered either way I am happy to change it.

No extras spaces are needed around any of the `*` in the line
    `z = np.cos(1.5*x)*np.cos(1.5*y)`
From PEP8: "If operators with different priorities are used, consider adding whitespace around the operators with the lowest priority(ies). Use your own judgement".  There are no operator priorities causing confusion here; the line is fine as it is.  I assume you are using the `pep8` tool which is sometimes a little too enthusiastic - it's recommendation of
    `z = np.cos(1.5 * x) * np.cos(1.5 * y)`
is very poor.