A SearchableSelect widget for Textual, that's composed of an Input and an OptionList, and acts as a regular Select widget. Allows searching for items in the options, which is not possible with the base Select widget.

searchableselect.py

from typing import Any

from textual.containers import Vertical, VerticalScroll
from textual.widgets import Select, OptionList, Input
from textual.widgets.option_list import Option
from textual.validation import Validator, ValidationResult


class InputInOptions(Validator):
    """An `Input` validator that checks if the input is part of a list."""
    def __init__(self, options, *args, **kwargs):
        self.options = options
        super().__init__(*args, **kwargs)

    def validate(self, value: str) -> ValidationResult:
        return self.success() if value in self.options else self.failure(f"Value '{value}' is not valid.")


class SearchableSelect(Vertical):
    def __init__(self, options: dict[str:Any]|list[Any]|list[tuple], sort: bool = True, *args, **kwargs):
        # Handle options
        # If it is a dict, create a list of `Option` instances with key as `id` and value as `prompt`
        if isinstance(options, dict):
            if sort:
                options = {k: options[k] for k in sorted(options.keys())}  # sort by key
            options = [Option(v, id=k) for k,v in options.items()]

        # If it is a list...
        elif isinstance(options, list):
            # ... of tuples, ie. same way of creating a regular `Select`, where `options` is of type list[tuple]
            # then, same as for dict: create a list of `Option` instances with key as `id` and value as `prompt`
            if isinstance(options[0], tuple):
                # Name is index 0, id is index 1 (just as for `Select`)
                if sort:
                    options.sort(key=lambda tup: tup[1])  # Reorder by id, ie. index 1
                options = [Option(tup[0], id=tup[1]) for tup in options]

            # ... of other elements, create a list of `Option` instances with both prompt and id being the element
            else:
                if sort:
                    options.sort()
                options = [Option(element, id=element) for element in options]

        self.all_options = options
        self.option_list = OptionList(*options)

        self.input = Input(validators=InputInOptions([option.prompt for option in options]))
        self.input.selected_option_id = None

        super().__init__(self.input, VerticalScroll(self.option_list), *args, **kwargs)

    @property
    def value(self):
        return self.input.selected_option_id

    def on_input_changed(self, event: Input.Changed) -> None:
        self.option_list.styles.display = 'block'
        options: list[Option]

        if event.value:
            query = Matcher(event.value)
            options = [
                option
                for option in self.all_options
                if query.match(option.prompt) > 0.99  # match by `id` or `prompt` ?
            ]
        else:
            options = self.all_options

        self.option_list.clear_options()
        self.option_list.add_options(options)

    def on_option_list_option_selected(self, event: OptionList.OptionSelected) -> None:
        with self.input.prevent(Input.Changed):
            self.input.value = event.option.prompt
            self.input.selected_option_id = event.option_id
        self.option_list.styles.display = 'none'
        self.post_message(Select.Changed(self, event.option_id))

This helped me figure out something similar that was kicking my butt. Thanks for publishing!