Textualize/textual · error · InvalidLineStyle

Valid rule line styles are {friendly_list(_VALID_LINE_STYLES

Error message

Valid rule line styles are {friendly_list(_VALID_LINE_STYLES)}

What it means

Raised by Rule.validate_line_style reactive validator when line_style is not in _VALID_LINE_STYLES (e.g. 'solid', 'heavy', 'double', 'dashed', ... — see the module constants). Assignment of an unknown style raises InvalidLineStyle at set time.

Source

Thrown at src/textual/widgets/_rule.py:195

                f"Valid rule orientations are {friendly_list(_VALID_RULE_ORIENTATIONS)}"
            )

    def watch_orientation(
        self, old_orientation: RuleOrientation, orientation: RuleOrientation
    ) -> None:
        self.remove_class(f"-{old_orientation}")
        self.add_class(f"-{orientation}")

    def validate_orientation(self, orientation: RuleOrientation) -> RuleOrientation:
        if orientation not in _VALID_RULE_ORIENTATIONS:
            raise InvalidRuleOrientation(
                f"Valid rule orientations are {friendly_list(_VALID_RULE_ORIENTATIONS)}"
            )
        return orientation

    def validate_line_style(self, style: LineStyle) -> LineStyle:
        if style not in _VALID_LINE_STYLES:
            raise InvalidLineStyle(
                f"Valid rule line styles are {friendly_list(_VALID_LINE_STYLES)}"
            )
        return style

    def get_content_width(self, container: Size, viewport: Size) -> int:
        if self.orientation == "horizontal":
            return container.width
        return 1

    def get_content_height(self, container: Size, viewport: Size, width: int) -> int:
        if self.orientation == "horizontal":
            return 1
        return container.height

    @classmethod
    def horizontal(
        cls,
        line_style: LineStyle = "solid",

View on GitHub (pinned to 06dbeef4bb)

Solutions

1. Check _VALID_LINE_STYLES in textual/widgets/_rule.py and use an exact name (e.g. 'solid', 'heavy', 'dashed').
2. Avoid inventing styles; pick the closest valid one.
3. Pin/verify your Textual version's supported styles.

Example fix

# before
Rule(line_style='dotted')
# after
Rule(line_style='dashed')

from textual.widgets._rule import _VALID_LINE_STYLES
assert style in _VALID_LINE_STYLES

def is_line_style(s: str) -> bool: return s in _VALID_LINE_STYLES

When it happens

Trigger: Rule(line_style='dotted') or rule.line_style = 'ascii' where those names are not in the valid set.

Common situations: Guessing style names, copying styles valid in CSS borders but not Rule, or Textual version differences in supported styles.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Valid rule orientations are {friendly_list(_VALID_RULE_ORIEN
• {self.name} must be a str (e.g. '10%') or a float (e.g. 0.1)
• Expected a character or hatch value here; found {character!r
• {token!r} is not a valid scalar
• {name!r} is an invalid {description}; identifiers must conta

AI-assisted analysis of Textualize/textual@06dbeef4bb (2026-08-27). Data as JSON: /api/errors/69a5d78deed4bc59. Report an issue: GitHub.