fix(engine): fix labware gripperOffsets not allowing only a default offset

[jbleon95]

Overview

As introduced in #13186, labware definitions can have a gripperOffsets property for providing an offset when picking up and dropping labware to and from that labware. It is required to have a default field, used for anything that does not have a specific slot name (e.g. SLOT_C1).

It was noticed in testing though that that default key, if there was no corresponding slot name key, was producing a KeyError because it was always attempting a direct access of the slot name key, regardless if it existed or not. This PR fixes that by first checking for the presence of the key before going for a direct access. This is not currently affecting any existing definition since the only one (opentrons_universal_flat_adapter) has all possible slot names it can be in in its gripperOffsets

Test Plan

Tested to make sure that a definition with a default only entry worked and did not crash, that gripping to and from a flat adapter still worked as expected, and that gripping to and from a labware with no offset continued to work.

Used this protocol with and without adding a default gripper offset to the aluminum block:

metadata = {
    'protocolName': 'Labware GripperOffsets test',
}

requirements = {
    "robotType": "OT-3",
    "apiLevel": "2.15"
}


def run(context):
    heater_shaker = context.load_module("heaterShakerModuleV1", location="D1")
    temp_module = context.load_module("temperatureModuleV2", location="D3")

    flat_adapter = heater_shaker.load_adapter("opentrons_universal_flat_adapter")
    aluminum_block = temp_module.load_adapter("opentrons_96_well_aluminum_block")

    corning_plate = context.load_labware("corning_384_wellplate_112ul_flat", location="C1")
    nest_plate = context.load_labware("nest_96_wellplate_100ul_pcr_full_skirt", location="C3")

    heater_shaker.open_labware_latch()

    context.move_labware(corning_plate, new_location=flat_adapter, use_gripper=True)
    context.home()
    heater_shaker.close_labware_latch()
    heater_shaker.open_labware_latch()
    context.move_labware(corning_plate, new_location="C1", use_gripper=True)


    context.move_labware(nest_plate, new_location=aluminum_block, use_gripper=True)
    context.home()
    context.move_labware(nest_plate, new_location="C3", use_gripper=True)

  "gripperOffsets": {
    "default": {
      "pickUpOffset": {
        "x": 0,
        "y": 0,
        "z": 0
      },
      "dropOffset": {
        "x": 0,
        "y": 0,
        "z": 10
      }
    }

Changelog

• Fixed get_labware_gripper_offsets to check for presence of key before accessing it from parsed_offsets

Review requests

Risk assessment

Low, this fixes an exception that was being raised but otherwise does not change the function's behavior.

[SyntaxColoring]

Fix makes sense to me. Thanks! One unrelated question about this area of the code.