fix(api): prevent protocols from passing with mistyped property setting for liquid classes

[jbleon95]

Overview

This PR addresses an issue found while testing liquid classes. The API for changing individual liquid class properties uses the @property.setter decorator to allow easy one line changes of properties while validating the values that the properties are being set to. A consequence of this is because Python allows dynamic setting of variables, a typo (e.g putting water_p50_props.aspirate.mix.enable = True instead of water_p50_props.aspirate.mix.enabled = True) did not cause the protocol to fail analysis. This means that a multi-hour protocol could not behave as expected due to a typo somewhere in the protocol.

Since this would be a huge pain point for customers, the liquid class properties now use the slots=True argument of dataclass to automatically generate the __slots__ attribute, preventing instances from being assigned new variables while giving a small, though negligible, performance boost.

Test Plan and Hands on Testing

This protocol now fails analysis with a AttributeError [line 16]: 'MixProperties' object has no attribute 'enable' error. Fixing line 16 to be enabled causes the protocol to correctly pass.

requirements = {
	"robotType": "Flex",
	"apiLevel": "2.22"
}

def run(protocol_context):
	tiprack1 = protocol_context.load_labware("opentrons_flex_96_tiprack_50ul", "C1")
	trash = protocol_context.load_trash_bin('A3')
	pipette_50 = protocol_context.load_instrument("flex_1channel_1000", "right", tip_racks=[tiprack1])

	nest_plate = protocol_context.load_labware("nest_96_wellplate_100ul_pcr_full_skirt", "D3")
	arma_plate = protocol_context.load_labware("armadillo_96_wellplate_200ul_pcr_full_skirt", "D2")

	water_class = protocol_context.define_liquid_class("water")
	water_p50_props = water_class.get_for("flex_1channel_1000", "opentrons_flex_96_tiprack_50ul")
	water_p50_props.aspirate.mix.enable = True  # This is a typo

Changelog

• Disallow setting non-existent properties for liquid class property dataclasses

Risk assessment

Low

[ddcc4]

Hey, if your goal is to define a class where no new fields can be created dynamically, can you look into using slots?

(I haven't had a chance to dig through it to see if it would work for our use case, but that's what slots are for.)

[SyntaxColoring]

Nice. Thank you both!

[sanni-t]

Awesome!