Missing usage of slots in classes with DAQmx attributes

[zhindes]

A few classes that contain DAQmx attributes are missing slots declarations. This can cause confusion if a user typo's one of our attribute names and then nothing useful happens.

For example, this code doesn't do what you expect, because the attribute is called samp_quant_samp_per_chan even though the cfg_implicit_timing function variable name is samps_per_chan for the same setting. Fun!

with nidaqmx.Task() as co_task:
    co_task.co_channels.add_co_pulse_chan_freq("Dev1/ctr0", freq=10000, duty_cycle=0.5)
    co_task.co_channels.all.co_pulse_term = ""
    co_task.timing.cfg_implicit_timing(sample_mode=nidaqmx.constants.AcquisitionType.FINITE, samps_per_chan=256)

    for i in range(0, 100):
        number_of_samples = random.randint(2, 256)

        # Update the CO task
        co_task.timing.samps_per_chan = number_of_samples # <-- THIS IS DOING NOTHING!
        print(f"Number of samples: {co_task.timing.samps_per_chan}")
        co_task.start()
        co_task.wait_until_done()
        co_task.stop()

Templates that have attributes that don't have slots (bad!):

• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/system/_watchdog_modules/expiration_state.py.mako
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/system/system.py.mako
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/system/watchdog.py.mako
• All of https://github.com/ni/nidaqmx-python/tree/master/src/codegen/templates/task/triggering
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/task/_export_signals.py.mako
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/task/_in_stream.py.mako
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/task/_out_stream.py.mako
• https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/task/_timing.py.mako
• Not a template, but https://github.com/ni/nidaqmx-python/blob/master/src/handwritten/task/_task.py

There are some iffy ones... e.g., collections don't have properties, only functions. But maybe they should have slots not to confuse people? idk. https://github.com/ni/nidaqmx-python/blob/master/src/codegen/templates/task/collections/_ai_channel_collection.py.mako. I think starting with that list above is good enough for now.

Note: this was create in response to an internal issue: Bug 2924340: Setting non-existent attribute on the CO timing does not cause assertion in python

[bkeryan]

FYI, https://stackoverflow.com/questions/472000/usage-of-slots has some interesting details:

• You can still allow creating new fields if you add __dict__ to slots. We would want to avoid this.
• Similarly, slots disables weakref support unless you add __weakref__ to slots. It may make sense to continue to allow weak references to Task objects, if nothing else.
• Setting slots may interfere with assigning __class__ unless the slots match. I don't think this is a problem because we only do this with subclasses and all of the subclasses set slots already.