Tab key behavior inconsistent between machines

[JonDehn]

I have an application that I can run on different laptops, both are at the same level of python (3.14) and OS version. In the app there is a ModalScreen with several input fields, gathered into vertical and horizontal boxes. On one machine, the tab key advance from one field to the next, as would be expected. On the other, it does nothing. I have not (as far as I can tell) done anything to change the default behavior of the tab key. Any idea what could be causing this discrepancy? The app is large, and I'm not sure I can create a small example that would exhibit the same behavior, so I have not included any sample code.

[nicholas-greenwood]

i'd check whether tab reaches textual before trying to reduce the app

in the same terminal and environment you use to launch the app on each laptop, run textual keys and press tab. if the command's missing, it comes from textual-dev

if one laptop doesn't report key='tab', i'd check that terminal's shortcuts and os key settings first

if both report it, i'd compare the installed textual versions before narrowing down the app's focus handling. matching python and os versions don't tell us whether textual matches

does textual keys report key='tab' on both laptops?

[JonDehn]

I did a little more digging. The 'textual keys' does report the tab key on both laptops. Both are running textual 8.0.0.
The difference is a different configuration parameter passed to the same program on the two different laptops. One has a full set of enabled actions (the options at the bottom of the window). The tab key works in that case.

The other has an option that disables some of those actions, using this code:

def check_action(self, action: str, parameters: tuple[object, ...]) -> bool | None:
    # disable those actions not needed when used only for checkout
    if self.checkout_only:
        if action not in self.CHECKOUT_ONLY:
            return False
    return True

(The names of the action keys are checked against a constant list (CHECKOUT_ONLY), sometimes a true is returned, sometimes false.)

If this returns false sometimes, it appears that the tab key isn't working in the modalScreen that pops up.
So I guess change the way the list of actions is trimmed down to have have those unused ones at all when the configuration parameters is passed in, rather than "disabling" them via check_action. Although it would be nice to know why this method doesn't work.

[JonDehn]

So I just figured it out (I think). My "check_action" code disabled a bunch of pre-defined actions, one of which must have controlled the tab key. Disabling only the actions that I defined, but didn't want in my "reduced action" mode fixed that problem.

Thanks for causing me to think this through thoroughly