# Source code for scrapy.selector.unified

    """
    XPath selectors based on lxml
    """

    from __future__ import annotations

    from typing import Any

    from parsel import Selector as _ParselSelector

    from scrapy.http import HtmlResponse, TextResponse, XmlResponse
    from scrapy.utils.python import to_bytes
    from scrapy.utils.response import get_base_url
    from scrapy.utils.trackref import object_ref

    __all__ = ["Selector", "SelectorList"]

    _NOT_SET = object()

    def _st(response: TextResponse | None, st: str | None) -> str:
        if st is None:
            return "xml" if isinstance(response, XmlResponse) else "html"
        return st

    def _response_from_text(text: str | bytes, st: str | None) -> TextResponse:
        rt: type[TextResponse] = XmlResponse if st == "xml" else HtmlResponse
        return rt(url="about:blank", encoding="utf-8", body=to_bytes(text, "utf-8"))

    class SelectorList(_ParselSelector.selectorlist_cls, object_ref):
        """
        The :class:`SelectorList` class is a subclass of the builtin ``list``
        class, which provides a few additional methods.
        """

    class Selector(_ParselSelector, object_ref):
        """
        An instance of :class:`Selector` is a wrapper over response to select
        certain parts of its content.

        ``response`` is an :class:`~scrapy.http.HtmlResponse` or an
        :class:`~scrapy.http.XmlResponse` object that will be used for selecting
        and extracting data.

        ``text`` is a unicode string or utf-8 encoded text for cases when a
        ``response`` isn't available. Using ``text`` and ``response`` together is
        undefined behavior.

        ``type`` defines the selector type, it can be ``"html"``, ``"xml"``, ``"json"``
        or ``None`` (default).

        If ``type`` is ``None``, the selector automatically chooses the best type
        based on ``response`` type (see below), or defaults to ``"html"`` in case it
        is used together with ``text``.

        If ``type`` is ``None`` and a ``response`` is passed, the selector type is
        inferred from the response type as follows:

        * ``"html"`` for :class:`~scrapy.http.HtmlResponse` type
        * ``"xml"`` for :class:`~scrapy.http.XmlResponse` type
        * ``"json"`` for :class:`~scrapy.http.TextResponse` type
        * ``"html"`` for anything else

        Otherwise, if ``type`` is set, the selector type will be forced and no
        detection will occur.
        """

        __slots__ = ["response"]
        selectorlist_cls = SelectorList

        def __init__(
            self,
            response: TextResponse | None = None,
            text: str | None = None,
            type: str | None = None,  # noqa: A002
            root: Any | None = _NOT_SET,
            **kwargs: Any,
        ):
            if response is not None and text is not None:
                raise ValueError(
                    f"{self.__class__.__name__}.__init__() received both response and text"
                )

            st = _st(response, type)

            if text is not None:
                response = _response_from_text(text, st)

            if response is not None:
                text = response.text
                kwargs.setdefault("base_url", get_base_url(response))

            self.response = response

            if root is not _NOT_SET:
                kwargs["root"] = root

            super().__init__(text=text, type=st, **kwargs)