attrs slotted classes

[rafmudaf]

The core simulation code of FLORIS largely uses attrs for creating the infrastructure to initialize the low level classes. One feature of attrs is that it by default creates slotted classes which improve performance in CPython.

The attrs documentation says slotted classes do not support monkey patching:

It’s not possible to monkeypatch methods on slotted classes. This can feel limiting in test code, however the need to monkeypatch your own classes is usually a design smell.

This was a surprise because I have a strong hunch that we have some monkey-patched code in places.

In an attempt to test this feature, I changed the following unit test in the FlowField unit tests:

def test_n_wind_speeds(flow_field_fixture):
    flow_field_fixture.asdf = 2         # Monkey patch an attribute
    flow_field_fixture.initialize_velocity_field = test_n_wind_directions     # Monkey patch a method
    assert flow_field_fixture.n_wind_speeds > 0

No error was raised despite FlowField being an attrs-class.