Textualize/textual · error · ScalarResolveError

expected dimensions; found

Error message

expected dimensions; found {str(self)!r}

What it means

Raised by Scalar.resolve when the scalar's unit has no entry in RESOLVE_MAP, i.e. the unit cannot be resolved to a dimension in the current context (typically a percent/relative unit resolved without a reference size).

Solutions

1. Construct scalars via Scalar.parse or Scalar.from_number instead of manual unit combos
2. Ensure you pass a concrete size when resolving percent-based scalars
3. Check that unit and percent_unit arguments are compatible (both dimensionful or both fractional)

Example fix

// before
scalar = Scalar(50.0, Unit.PERCENT, Unit.PERCENT)
scalar.resolve(None, viewport)
// after
scalar = Scalar(50.0, Unit.PERCENT, Unit.CELLS)
scalar.resolve(container_width, viewport)

from textual.css.scalar import Scalar
def resolvable(scalar: Scalar) -> bool:
    from textual.css.scalar import RESOLVE_MAP
    return scalar.unit in RESOLVE_MAP

from textual.css.scalar import ScalarResolveError
try:
    dim = scalar.resolve(size, viewport)
except ScalarResolveError:
    dim = scalar.resolve(size, viewport, percent_unit=Unit.CELLS)

When it happens

Trigger: Calling scalar.resolve(size, viewport, fraction_unit) where scalar has a unit (e.g. Unit.PERCENT as percent_unit) but the corresponding resolver is missing from RESOLVE_MAP — commonly resolving a scalar that was constructed with mismatched units, or resolving CELLS/percent units without proper dimension context.

Common situations: Manually constructing Scalar objects with inconsistent unit/percent_unit arguments; resolving a scalar captured from a different layout context; version changes that add new units not present in RESOLVE_MAP.

Related errors

• is not a valid scalar
• cannot mix 'none' with other style flags
• DeclarationError(error.name, error.token, error.message)
• DeclarationError(name, token, message)
• (found ). ; Did you forget a semicolon at the end of a line?

AI-assisted analysis of Textualize/textual@06dbeef4bb (2026-08-27). Data as JSON: /api/errors/30d05893931cc7de. Report an issue: GitHub.

Appendix: source

Thrown at src/textual/css/scalar.py:291

            size: Size of the container.
            viewport: Size of the viewport (typically terminal size)

        Raises:
            ScalarResolveError: If the unit is unknown.

        Returns:
            A size (in cells)
        """
        value, unit, percent_unit = self

        if unit == Unit.PERCENT:
            unit = percent_unit
        try:
            dimension = RESOLVE_MAP[unit](
                value, size, viewport, fraction_unit or _FRACTION_ONE
            )
        except KeyError:
            raise ScalarResolveError(f"expected dimensions; found {str(self)!r}")
        return dimension

    def copy_with(
        self,
        value: float | None = None,
        unit: Unit | None = None,
        percent_unit: Unit | None = None,
    ) -> Scalar:
        """Get a copy of this Scalar, with values optionally modified

        Args:
            value: The new value, or None to keep the same value
            unit: The new unit, or None to keep the same unit
            percent_unit: The new percent_unit, or None to keep the same percent_unit
        """
        return Scalar(
            value if value is not None else self.value,
            unit if unit is not None else self.unit,

View on GitHub (pinned to 06dbeef4bb)