Undo step with IdaPython?

No. Only interactive user actions can be undone via the UI or keyboard shortcut.

In the IDA Pro 9.0 changelog is the entry:

SDK: published basic undo interface (create undo point, undo, redo)

And from there I found that ida_undo had been added to the Python SDK. It has the routine create_undo_point(*args). The documentation suggests it might accept two arguments bytes and size; however, this is incorrect.

There's a use in the ida-domain API of the routine:

        if probe_only:
            ida_undo.create_undo_point('ida_domain_flirt', 'undo_point')
        ida_funcs.plan_to_apply_idasgn(str(path))
        ida_auto.auto_wait()
        hooks.unhook()
        results = hooks.results
        if probe_only:
            ida_undo.perform_undo()

and details in the raw SWIG bindings.

In reality, this function seems to have the signature:

def create_undo_point(action_name: str, label: str) -> bool

I'm not sure how action_name is used, but label is used to set the "undo action label" which can be seen in the Edit→Undo... menu, and is accessible from ida_undo.get_undo_action_label() -> str.

So, programmatically, you can do something like:

ida_undo.create_undo_point("???", "yolo")

... bunch of stuff ...

while ida_undo.get_undo_action_label() != "yolo":
    ida_undo.perform_undo()

Specifically, the following IDA Python script demonstrates using the undo APIs:

import ida_undo
import ida_name


ida_name.set_name(0x10001000, "foo")
assert ida_name.get_name(0x10001000) == "foo"

ida_undo.create_undo_point("???", "my_undo_point")
assert ida_undo.get_undo_action_label() == "my_undo_point"

ida_name.set_name(0x10001000, "bar")
assert ida_name.get_name(0x10001000) == "bar"

ida_undo.perform_undo()
assert ida_name.get_name(0x10001000) == "foo"