xtb_step Phase C – xTBParameters Fix Drop – File Drop Notes

This drop fixes the TypeError: 'NoneType' object is not subscriptable that you saw when adding the xTB step to a flowchart. The root cause was that the cookiecutter never created an xTBParameters class for the top-level step, and xTB.__init__() never set self.parameters, so seamm.tk_node.create_dialog blew up trying to read self.node.parameters["extra keywords"].

This is the same pattern that fhi_aims_step uses: the top-level step has a (mostly empty) Parameters subclass whose only job is to satisfy the GUI machinery. The substeps own all the real parameters.

Three small changes

You only need to apply three changes on top of your current installed tree (which is already Phase A + the Phase B substep work plus the installer drop):

New file

xtb_step/xtb_parameters.py

Minimal xTBParameters(seamm.Parameters) subclass with an empty parameters dict. Mirrors fhi_aims_step/fhi_aims_parameters.py structurally. The "extra keywords" entry that the dialog code reads is supplied automatically by the seamm.Parameters base class – the subclass does not need to declare it.

One-line change to xtb_step/xtb.py

In xTB.__init__(), immediately after the super().__init__(...) call (which ends with )  # yapf: disable), add:

self.parameters = xtb_step.xTBParameters()

so that block looks like:

super().__init__(
    flowchart=flowchart,
    title="xTB",
    extension=extension,
    module=__name__,
    logger=logger,
)  # yapf: disable

self.parameters = xtb_step.xTBParameters()
self._metadata = xtb_step.metadata

(I’m including a full Phase-A-compatible xtb.py in this drop too, in case it’s easier to overwrite than patch – but the only change relative to Phase A is the one new line.)

One-line change to xtb_step/__init__.py

Add an import for xTBParameters right after the existing xTBStep import. The change is a single new line:

from .xtb import xTB  # noqa: F401, E501
from .xtb_step import xTBStep  # noqa: F401, E501
from .xtb_parameters import xTBParameters  # noqa: F401     <-- new
from .tk_xtb import TkxTB  # noqa: F401, E501

(Again, the full updated __init__.py is included in this drop for copy-and-replace convenience.)

What this should fix

After the change, opening the edit dialog on the top-level xTB step in a flowchart should produce a (mostly empty) parameter dialog instead of a stack trace. The dialog will be empty because the top-level step genuinely has no parameters of its own – all the real parameters live on the Energy / Optimization / Frequencies substeps inside the subflowchart, exactly like FHI-aims.

Why didn’t this come up in Phase A?

Phase A’s testing was “does the plug-in install and does the test suite pass?”. Both of those operate without ever calling tk_node.create_dialog on the top-level step (the test harness constructs nodes but doesn’t open Tk dialogs, and make install doesn’t touch Tk at all). The bug only surfaced when you actually clicked on the step in the flowchart GUI – which is the first time create_dialog runs on the top-level step.

Lesson: the cookiecutter has a small gap for the subflowchart variant where it generates substep parameter classes but not a top-level one. Worth flagging for the SEAMM cookiecutter maintainers (you, presumably).

Code style

All files compile cleanly. The new xtb_parameters.py follows the same docstring/header pattern as the other parameter files in the plug-in. All lines are <= 88 characters.