DataTable height issue

[Tinche]

Hi, it appears to me the DataTable widget has an issue with calculating its height.

Here's a MRE:

from textual.app import App, ComposeResult
from textual.containers import Vertical
from textual.widgets import DataTable, Input


class MyApp(App):
    def compose(self) -> ComposeResult:
        with Vertical():
            yield Input()
            table = DataTable[str](id="table")
            table.add_columns("name", "value")
            yield table

    def on_mount(self) -> None:
        self.query_exactly_one("#table", DataTable).add_rows([(i, i) for i in range(100)])


if __name__ == "__main__":
    MyApp().run()

Run this, tab over to the DataTable and try scrolling down. If the DataTable has greater height than the terminal, it will scroll, but there will be 3 rows off screen, at the bottom. The Input widget takes up 3 rows, so that might be a clue.

# Textual Diagnostics

## Versions

| Name    | Value  |
|---------|--------|
| Textual | 1.0.0  |
| Rich    | 13.5.2 |

## Python

| Name           | Value                                                |
|----------------|------------------------------------------------------|
| Version        | 3.12.4                                               |
| Implementation | CPython                                              |
| Compiler       | Clang 16.0.0 (clang-1600.0.26.3)                     |
| Executable     | /Users/tintvrtkovic/ha/nlu_pipeline/.venv/bin/python |

## Operating System

| Name    | Value                                                                                            |
|---------|--------------------------------------------------------------------------------------------------|
| System  | Darwin                                                                                           |
| Release | 24.1.0                                                                                           |
| Version | Darwin Kernel Version 24.1.0: Thu Oct 10 21:02:27 PDT 2024; root:xnu-11215.41.3~2/RELEASE_X86_64 |

## Terminal

| Name                 | Value       |
|----------------------|-------------|
| Terminal Application | Kitty       |
| TERM                 | xterm-kitty |
| COLORTERM            | truecolor   |
| FORCE_COLOR          | *Not set*   |
| NO_COLOR             | *Not set*   |

## Rich Console options

| Name           | Value                |
|----------------|----------------------|
| size           | width=319, height=42 |
| legacy_windows | False                |
| min_width      | 1                    |
| max_width      | 319                  |
| is_terminal    | True                 |
| encoding       | utf-8                |
| max_height     | 42                   |
| justify        | None                 |
| overflow       | None                 |
| no_wrap        | False                |
| highlight      | None                 |
| markup         | None                 |
| height         | None                 |

[willmcgugan]

The DataTable has a height of auto. i.e. it will grow as you add rows. It has a max-height of 100%, which will mean it won't grow larger than the height of the container.

If you want the DT to use the remaining height, set its height to 1fr.

[Tinche]

Got it, thanks!