Set bindings on widget instance rather than class

[pawamoy]

I develop an app that looks like a Kanban board. It has 3 or 4 default columns. I allow users to configure the columns with a Python script in their user config directory. I would like them to be able to specify the keybindings they want without having to subclass my Column class. Instead, I'd like that they can pass bindings when instantiating a Column class. So this

from kanbanthing import Column

columns = [
    Column("One", bindings=[("a", "process_one", "Do something with current row")]),
    Column("Two", bindings=[("b", "process_one", "Do something else with current row")]),
]

...instead of this

from kanbanthing import Column


class ColumnOne(Column):
    BINDINGS = [("a", "process_one", "Do something with current row")]


class ColumnTwo(Column):
    BINDINGS = [("b", "process_one", "Do something else with current row")]


columns = [
    ColumnOne("One"),
    ColumnTwo("Two"),
]

(notice how the second example has much more boilerplate code, declaring custom classes that are eventually instantiated only once)

(my Column class declares the process_one action itself)

I tried setting bindings in Column.__init__ like this:

def __init__(self, bindings):
        self.BINDINGS = bindings

...but Textual does not seem to pick up the bindings (they don't show up in the footer, and they don't trigger anything). I suppose it gets the BINDINGS attribute from the widget's class and not the instance? And I suppose there is way to manually re-bind everything when the focus moves between widgets (columns)? I see App has a bind method, so I can add bindings of the newly focused column, but how can I remove the bindings of the previously focused one?

I suppose I could also dynamically declare the subclasses myself 🤔

[pawamoy]

OK, I was able to dynamically create subclasses within the __new__ method of my Column class, satisfying Textual's expectations:

class Column(Container):
    _count = 0

    def __new__(cls, *args, **kwargs) -> Column:
        Column._count += 1
        bindings = kwargs.pop("bindings", [])
        custom_column_class = type(f"Column{Column._count}", (Column,), {"BINDINGS": bindings})
        return super().__new__(custom_column_class)

    def __init__(
        self,
        *,
        title: str,
        headers: Sequence[str],
        producer: Callable,
        consumer: Callable | None = None,
        bindings: list[tuple[str, str, str]] | None = None,  # noqa: ARG002
        **kwargs,
    ) -> None:
        ...

That will do for now 🙂 Note that I'd still find widget instance bindings very useful 😄