A while ago I posted about having trouble with an auto-resizing DataTable. Here's the best I got now for anyone else.

[nannerpusser]

I believe auto-resizing columns that fill the container/screen width are a feature we'll see implemented officially, but in the meantime I have a half-jank but working and stable way to handle it if anyone needs it or just an idea from seeing it. For reference I use this to return search results from an API with variable length ("width") of cell row content and two different justify styles for three total column headers (always visible, no row label display):

from rich.text import Text
from textual.widgets import DataTable
from textual import events
from textual import log


class AutoResizingDataTable(DataTable):
	#measurement is cells, SEPARATOR_ESTIMATE is the tweakable you can adjust depending on what you do with your Text renderable and/or Label widgets in header slots

    MIN_COL_WIDTH = 4
    SEPARATOR_ESTIMATE = 3

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def _measure_render_width(self, value) -> int:
        text = Text(str(value))
        meas = text.cell_len if text else None
        return max(int(meas or 0), len(str(value)))

	#This was ultimately useless to me but only because I implemented justify in  a method on parent 
    def _ensure_header_justify(self, justify: str = "left") -> None:
        for col in self.columns.values():
            if hasattr(col, "label") and hasattr(col.label, "justify"):
                col.label.justify = justify

	#Still lots of room to clean this up and cut out fat. I wanted readability and no spaghetti above brevity 
    def auto_resize_columns(self, total_width: int | None = None) -> None:
        cols_keys = list(self.columns)  # ordered keys
        n = len(cols_keys)
        if n == 0:
            return

        if total_width is None:
            total_width = self.size.width
		#yeah, I know, incoming bad logic
        def _callback():
            self.app.set_timer(0.3, _callback, total_width)
            self.auto_resize_columns(total_width)

        # insert most "Textual" way to defer and wait on this because I was trying to KISS in  terms of when messages are sent/rec. and 		handled 
        if not total_width or total_width <= 0:
            self.app.set_timer(0.3, _callback, total_width)
            return

        mins = []
        for key in cols_keys:
            col = self.columns[key]
            header_label = getattr(col, "label", key)

            header_w = self._measure_render_width(header_label)
            mins.append(max(self.MIN_COL_WIDTH, header_w))

        usable = max(0, total_width - self.SEPARATOR_ESTIMATE * (n - 1))
        total_min = sum(mins)
        assigned = [0] * n

        if total_min >= usable:
            # scale down proportionally but keep a tiny bottom
            scale = usable / total_min if total_min > 0 else 0
            for i in range(n):
                assigned[i] = max(3, int(mins[i] * scale))
            diff = usable - sum(assigned)
            if diff > 0:
                assigned[-1] += diff
            elif diff < 0:
                assigned[-1] = max(3, assigned[-1] + diff)
        else:
            # give each its min then distribute remainder left->right
            assigned = list(mins)
            remainder = usable - sum(assigned)
            i = 0
            while remainder > 0:
                assigned[i % n] += 1
                remainder -= 1
                i += 1

        # apply by writing to Column.width and turning off auto_width, can be here or during mount on parent
        for idx, key in enumerate(cols_keys):
            col = self.columns[key]
            col.auto_width = False
            col.width = max(1, int(assigned[idx]))
        # Re-render
        try:
            self.refresh()
        except Exception:
            pass

    # integrate with resize event
    def on_resize(self, event: events.Resize) -> None:
        self.auto_resize_columns(event.size.width)

	#I implemented the Click handler for a custom ContextMenu right-click widget here. Get crazy with it