Clearing and adding data to `DataTable` without worker will cause it to sometime not display its content.

[kwevin]

Have you checked closed issues? https://github.com/Textualize/textual/issues?q=is%3Aissue+is%3Aclosed

• Yes

Please give a brief but clear explanation of the issue. If you can, include a complete working example that demonstrates the bug. Check it can run without modifications.

• When clearing and adding data to DataTable without using a Worker, the DataTable can sometime not properly display its content.

It will be helpful if you run the following command and paste the results:

textual diagnose

Textual Diagnostics

Versions

Name	Value
Textual	0.76.0
Rich	13.7.1

Python

Name	Value
Version	3.11.1
Implementation	CPython
Compiler	MSC v.1934 64 bit (AMD64)
Executable	C:\Users\Kevin\AppData\Local\pypoetry\Cache\virtualenvs\listentui-qruDwX8r-py3.11\Scripts\python.exe

Operating System

Name	Value
System	Windows
Release	10
Version	10.0.22621

Terminal

Name	Value
Terminal Application	Windows Terminal
TERM	Not set
COLORTERM	Not set
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=125, height=31
legacy_windows	False
min_width	1
max_width	125
is_terminal	True
encoding	utf-8
max_height	31
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

https://github.com/user-attachments/assets/1aecef14-a634-4f5d-a9cc-f310ea40a41e

mre is large because it contains some data, so it is in a gist https://gist.github.com/kwevin/18a543e54ff7336bb802d711481b1d72

[github-actions[bot]]

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

• Why doesn't the DataTable scroll programmatically?
• How do I fix WorkerDeclarationError?
• No widget called TextLog
• How can I select and copy text in a Textual app?

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

[willmcgugan]

Could you fix the formatting on the gist?

[TomJGooding]

It looks like the problem is the height=None on this line:

self.table.add_row(*rows, height=None)

This should "auto-detect the optimal height" but seems something isn't quite right.

Here's a more minimal example:

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

ROWS = [
    ("lane", "swimmer", "country", "time"),
    (4, "Joseph Schooling", "Singapore", 50.39),
    (2, "Michael Phelps", "United States", 51.14),
    (5, "Chad le Clos", "South Africa", 51.14),
    (6, "László Cseh", "Hungary", 51.14),
    (3, "Li Zhuhao", "China", 51.26),
    (8, "Mehdy Metella", "France", 51.58),
    (7, "Tom Shields", "United States", 51.73),
    (1, "Aleksandr Sadovnikov", "Russia", 51.84),
    (10, "Darren Burns", "Scotland", 51.84),
]

class ExampleApp(App):
    CSS = """
    DataTable {
        border: solid red;
    }
    """

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

    def on_mount(self) -> None:
        table = self.query_one(DataTable)
        table.add_columns(*ROWS[0])
        self.populate_table()

    def on_input_changed(self) -> None:
        self.populate_table()

    def populate_table(self) -> None:
        table = self.query_one(DataTable)
        table.clear()
        for row in ROWS[1:]:
            table.add_row(
                *row,
                height=None,
            )
        self.log.debug("Table populated")

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

[willmcgugan]

Yeah, I concur with @TomJGooding Looks like the auto height is breaking something.

[TomJGooding]

I confess I'm struggling to follow the code, but posting my findings in case it helps someone else fix this bug.

I think the problem is that when the virtual size is calculated, the self._y_offsets is an empty list:

https://github.com/Textualize/textual/blob/db3fda928ba3f4807f01ae24ecee260ce6206b1b/src/textual/widgets/_data_table.py#L1459-L1462

https://github.com/Textualize/textual/blob/db3fda928ba3f4807f01ae24ecee260ce6206b1b/src/textual/widgets/_data_table.py#L823-L826

Presumably because the row.height is still zero rather than the calculated height here?

https://github.com/Textualize/textual/blob/db3fda928ba3f4807f01ae24ecee260ce6206b1b/src/textual/widgets/_data_table.py#L818-L820

[mitaa]

I have quite a similar issue which might have the same cause. Not sure if I should open a new issue for that.

When the populate_table method is run for the first time (on startup) everything looks correct. When it's run for the second time (on_data_table_cell_selected) the auto-width of the columns is incorrect and column widths seem to correspond to the header.

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

ROWS = [
    ("lane", "swimmer", "country", "time"),
    (4, "Joseph Schooling", "Singapore", 50.39),
    (2, "Michael Phelps", "United States", 51.14),
    (5, "Chad le Clos", "South Africa", 51.14),
    (6, "László Cseh", "Hungary", 51.14),
    (3, "Li Zhuhao", "China", 51.26),
    (8, "Mehdy Metella", "France", 51.58),
    (7, "Tom Shields", "United States", 51.73),
    (1, "Aleksandr Sadovnikov", "Russia", 51.84),
    (10, "Darren Burns", "Scotland", 51.84),
]

class ExampleApp(App):
    def compose(self) -> ComposeResult:
        yield DataTable()

    def on_mount(self) -> None:
        self.populate_table()

    def on_data_table_cell_selected(self) -> None:
        self.populate_table()

    def populate_table(self) -> None:
        table = self.query_one(DataTable)
        table.clear(columns=True)
        table.add_columns(*ROWS[0])
        table.add_rows(ROWS[1:])
        self.log.debug("Table populated")

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

[TomJGooding]

@mitaa This looks like the same issue as #4470?

[mitaa]

@TomJGooding You're right! Sorry the confusion.

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