Textualize/textual · error · InvalidRuleOrientation

Valid rule orientations are {friendly_list(_VALID_RULE_ORIEN

Error message

Valid rule orientations are {friendly_list(_VALID_RULE_ORIENTATIONS)}

What it means

Raised by Rule.render when the orientation reactive is neither 'horizontal' nor 'vertical' — render handles horizontal and vertical branches and this else covers any other value. In practice it is hard to reach because validate_orientation also guards assignment, but a corrupted/orientation set via internals would hit it at render time.

Source

Thrown at src/textual/widgets/_rule.py:176

        self.orientation = orientation
        self.line_style = line_style
        self.expand = True

    def render(self) -> RenderResult:
        rule_character: str
        style = self.rich_style
        if self.orientation == "vertical":
            rule_character = _VERTICAL_LINE_CHARS[self.line_style]
            return VerticalRuleRenderable(
                rule_character, style, self.content_size.height
            )
        elif self.orientation == "horizontal":
            rule_character = _HORIZONTAL_LINE_CHARS[self.line_style]
            return HorizontalRuleRenderable(
                rule_character, style, self.content_size.width
            )
        else:
            raise InvalidRuleOrientation(
                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:

View on GitHub (pinned to 06dbeef4bb)

Solutions

1. Use only 'horizontal' or 'vertical' (the RuleOrientation literal values).
2. Assign through the public constructor/reactive so validate_orientation catches mistakes early.
3. Check _VALID_RULE_ORIENTATIONS in textual/widgets/_rule.py.

Example fix

# before
Rule(orientation='diag')
# after
Rule(orientation='horizontal')

def is_orientation(v: str) -> bool: return v in ('horizontal', 'vertical')

When it happens

Trigger: Rule(orientation='diagonal') or rule.orientation = 'up' — an invalid orientation string reaching render; typically blocked earlier by validate_orientation raising at assignment time.

Common situations: Passing a custom string that type-checks as RuleOrientation in loose typing, or bypassing validation via internal state.

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 line styles are {friendly_list(_VALID_LINE_STYLES
• {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/0d7cff1e2b8b1ffc. Report an issue: GitHub.