from typing import Any


def list_joined(separator_item: Any, items: list[Any]) -> list[Any]:
    """
    Like ", ".join(blah), except for lists.

    >>> list_joined("HI", ["yo", "cats"])
    ['yo', 'HI', 'cats']
    """
    return [
        part
        for early_item in items[:-1]
        for part in (early_item, separator_item)  # Weird syntax to flatten tuples.
    ] + items[-1:]