fix(api): Automatic tip tracking index out of range fix

[CaseyBatten]

Overview

Addresses RQA-2700

Automatic tip tracking when iterating through multiple tip racks did not take into account progression range across those tipracks resulting in the potential for an index out of range error to manifest under certain conditions. These changes seek to fix that.

Test Plan

Ensure that API 2.18 protocols consume tipracks without encountering an index out of range error manifesting as an out of tips error when iterating through multiple tipracks using tip-cluster based automatic tip tracking. Protocols such as the one below should execute without issue.

from opentrons import protocol_api
from opentrons.protocol_api import COLUMN, ALL

requirements = {
    "robotType": "Flex",
    "apiLevel": "2.18",
}



def run(ctx: protocol_api.ProtocolContext):

    tiprack1000_1 = ctx.load_labware("opentrons_flex_96_tiprack_1000ul", "B2")
    tiprack1000_2 = ctx.load_labware("opentrons_flex_96_tiprack_1000ul", "C2")

    pipette = ctx.load_instrument(
        "flex_96channel_1000", mount="left", tip_racks=[tiprack1000_1, tiprack1000_2]
    )

    trashA3 = ctx.load_trash_bin("A3")

    pipette.configure_nozzle_layout(style=COLUMN, start="A12", tip_racks=[tiprack1000_1, tiprack1000_2])

    # pickup and drop all 12 columns of the first tiprack and the first column of the second tiprack using Column A12 of the pipette (Should progress across the tiprack left to right)
    for x in range(13):
        pipette.pick_up_tip()
        pipette.drop_tip()
    
    pipette.configure_nozzle_layout(style=COLUMN, start="A1", tip_racks=[tiprack1000_1, tiprack1000_2])
    # pickup and drop the remaining 11 columns of the second tiprack using column A1 of the pipette (should progress right to left)
    for x in range(11):
        pipette.pick_up_tip()
        pipette.drop_tip()

Changelog

• Updated the tip cluster logic under tips.py to return None in situations where the iterator would extend beyond the bounds of a tiprack before the iteration logic has been able to evaluate the next upcoming step.

Review requests

Do these changes appear comprehensive enough given existing safegaurds within the tiprack iteration logic?

Risk assessment

Low, fixes oversight.

[vegano1]

Logically this makes sense.

[jbleon95]

These changes look like they'll solve the issue with tip tracking. Made a couple suggestions to potentially simplify these changes. If time allows I think a further refactor could simplify a lot of this logic, as well as going further since our whole tip tracking behavior is very spaghetti code to begin with.

[jbleon95]

This if statement could probably be removed and the while check be changed to while critical_column < len(columns) if I understand this correctly, since we're not doing any indexing immediately after this.

[jbleon95]

Same thing as above, except I don't think you'd need to change anything in the while conditional