Class query_one

src/textual/getters.py:62–150

Create a query one property. A query one property calls [Widget.query_one][textual.dom.DOMNode.query_one] when accessed, and returns a widget. If the widget doesn't exist, then the property will raise the same exceptions as `Widget.query_one`. Example: ```python from t

class query_one(Generic[QueryType]):
    """Create a query one property.

    A query one property calls [Widget.query_one][textual.dom.DOMNode.query_one] when accessed, and returns
    a widget. If the widget doesn't exist, then the property will raise the same exceptions as `Widget.query_one`.


    Example:
        ```python
        from textual import getters

        class MyScreen(screen):

            # Note this is at the class level
            output_log = getters.query_one("#output", RichLog)

            def compose(self) -> ComposeResult:
                with containers.Vertical():
                    yield RichLog(id="output")

            def on_mount(self) -> None:
                self.output_log.write("Screen started")
                # Equivalent to the following line:
                # self.query_one("#output", RichLog).write("Screen started")
        ```

    Args:
        selector: A TCSS selector, e.g. "#mywidget". Or a widget type, i.e. `Input`.
        expect_type: The type of the expected widget, e.g. `Input`, if the first argument is a selector.

    """

    selector: str
    expect_type: type["Widget"]

    @overload
    def __init__(self, selector: str) -> None:
        """

        Args:
            selector: A TCSS selector, e.g. "#mywidget"
        """

    @overload
    def __init__(self, selector: type[QueryType]) -> None: ...

    @overload
    def __init__(self, selector: str, expect_type: type[QueryType]) -> None: ...

    @overload
    def __init__(
        self, selector: type[QueryType], expect_type: type[QueryType]
    ) -> None: ...

    def __init__(
        self,
        selector: str | type[QueryType],
        expect_type: type[QueryType] | None = None,