Adding columns to empty `DataTable` won't appear?

[TomJGooding]

I'm not sure if this is a bug or possibly the intended behaviour for a empty DataTable (i.e. without rows).

Try pressing the c key with the app below to add new columns to the DataTable - notice they won't appear. Then press the r key to add a new row, then all columns will show.

EDIT: Actually this isn't specific only to an empty table, but rather new columns won't appear if there isn't any row with corresponding data in that column. Is that intentional?

from textual.app import App, ComposeResult
from textual.widgets import DataTable, Footer


class ExampleApp(App):
    BINDINGS = [
        ("c", "add_column", "Add Column"),
        ("r", "add_row", "Add Row"),
    ]

    column_number = 1

    def compose(self) -> ComposeResult:
        yield DataTable()
        yield Footer()

    def on_mount(self) -> None:
        table = self.query_one(DataTable)
        table.add_column(f"Column #{self.column_number}")
        self.column_number += 1

    def action_add_column(self) -> None:
        table = self.query_one(DataTable)
        table.add_column(f"Column #{self.column_number}")
        self.column_number += 1
        self.notify("No column added?", severity="error")

    def action_add_row(self) -> None:
        table = self.query_one(DataTable)
        table.add_row()
        self.notify("Now columns appear!", severity="information")


if __name__ == "__main__":
    app = ExampleApp()
    app.run()

[github-actions]

We found the following entries in the FAQ which you may find helpful:

• Why doesn't the DataTable scroll programmatically?
• How can I set a translucent app background?

Feel free to close this issue if you found an answer in the FAQ. Otherwise, please give us a little time to review.

This is an automated reply, generated by FAQtory

[TomJGooding]

Possibly related is #3449 where again perhaps the updates to column widths aren't being triggered?

[arcivanov]

I have worked around this via flipping show_header to True from False.