scrapy/scrapy · error · ValueError

{self.class.name}.init() received both response

Error message

{self.__class__.__name__}.__init__() received both response and text

What it means

Selector (scrapy.selector.Selector, the unified wrapper over parsel) raises ValueError in __init__ when both response and text are passed. A selector is constructed from exactly one source: a Response object (using its body/encoding) or a raw text string. Supplying both is ambiguous, so it is rejected immediately.

Source

Thrown at scrapy/selector/unified.py:71

    .. note:: JSON selector support requires ``parsel`` 1.8.0 or higher. With
       older versions setting ``type`` to ``"json"`` or ``"text"`` is not
       supported.
    """

    __slots__ = ["response"]
    selectorlist_cls = SelectorList

    def __init__(
        self,
        response: TextResponse | None = None,
        text: str | None = None,
        type: SelectorType | 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"
            )

        # A response that is neither HTML nor XML, e.g. a JSON one, keeps type
        # unset, so that parsel determines it from the body.
        if type is None:
            if isinstance(response, XmlResponse):
                type = "xml"  # noqa: A001
            elif response is None or isinstance(response, HtmlResponse):
                type = "html"  # noqa: A001

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

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

View on GitHub (pinned to 06af687662)

Solutions

Pass only one source: Selector(response=resp) or Selector(text=html_string).
In wrapper functions, branch on which argument is provided before constructing.
For raw bytes from a response, use response.text or let the response construct the selector itself (response.selector).

Example fix

# before
sel = Selector(response=response, text=response.text)  # ValueError

# after
sel = Selector(response=response)

Defensive patterns

Strategy: validation

Validate before calling

assert not (response is not None and text is not None), \
    'Selector accepts either response or text, not both'

Try / catch

try:
    sel = Selector(response=response, text=text)
except ValueError:
    sel = Selector(response=response) if response is not None else Selector(text=text)

Prevention

Pass exactly one of response or text.
In wrapper functions, branch on which argument is provided instead of forwarding both.
Prefer response.selector when you already hold the response.

When it happens

Trigger: Selector(response=resp, text='<html>...') or Selector(resp, text=html_string); helper functions that default both parameters and forward them unconditionally; copy-pasting shell examples into code with both kwargs filled.

Common situations: Wrapping selectors in utility functions where response and text both have defaults; feeding an encoded body string alongside the response for 'safety'; interactive scrapy shell habits carried into production code.

Related errors

AI-assisted analysis of scrapy/scrapy@06af687662 (2026-08-15). Data as JSON: /api/errors/00fb92c2b21000cc. Report an issue: GitHub.