pytest-dev/pytest · error · ValueError

is not a string or pytest.mark.* Marker

Error message

is not a string or pytest.mark.* Marker

What it means

Raised by Node.add_marker (via the marker path at lines 320-324) when the marker argument is neither a str nor a MarkDecorator. pytest accepts either a dotted-name string (resolved against MARK_GEN) or a MarkDecorator produced by pytest.mark.<name>. Any other type (int, dict, raw Mark, None) is rejected because it cannot be normalized to a marker.

Solutions

1. Pass a string marker name: node.add_marker('skip').
2. Pass a MarkDecorator from the mark generator: node.add_marker(pytest.mark.skip).
3. If you hold a raw Mark, wrap it: MarkDecorator(mark) before adding.

Example fix

// before
node.add_marker(my_mark.mark)
// after
from _pytest.mark import MarkDecorator
node.add_marker(MarkDecorator(my_mark.mark))

from _pytest.mark import MarkDecorator
assert isinstance(marker, (str, MarkDecorator))

def _is_valid_marker(marker) -> bool:
    from _pytest.mark import MarkDecorator
    return isinstance(marker, (str, MarkDecorator))

When it happens

Trigger: node.add_marker(42); node.add_marker({'name': 'skip'}); node.add_marker(some_mark.mark) passing a raw Mark instead of MarkDecorator; node.add_marker(None).

Common situations: Confusing Mark with MarkDecorator; passing a marker instance created via some_mark.args instead of pytest.mark.skip; programmatic marker construction errors.

Related errors

• warning must be an instance of Warning or subclass, got
• config is not a valid argument for from_parent
• config or parent must be provided
• nodeid or parent must be provided
• session is not a valid argument for from_parent

AI-assisted analysis of pytest-dev/pytest@0d6fbdeffa (2026-08-11). Data as JSON: /api/errors/0aa1a81270f1bbbe. Report an issue: GitHub.

Appendix: source

Thrown at src/_pytest/nodes.py:323

        chain.reverse()
        return chain

    def add_marker(self, marker: str | MarkDecorator, append: bool = True) -> None:
        """Dynamically add a marker object to the node.

        :param marker:
            The marker.
        :param append:
            Whether to append the marker, or prepend it.
        """
        from _pytest.mark import MARK_GEN

        if isinstance(marker, MarkDecorator):
            marker_ = marker
        elif isinstance(marker, str):
            marker_ = getattr(MARK_GEN, marker)
        else:
            raise ValueError("is not a string or pytest.mark.* Marker")
        self.keywords[marker_.name] = marker_
        if append:
            self.own_markers.append(marker_.mark)
        else:
            self.own_markers.insert(0, marker_.mark)

    def iter_markers(self, name: str | None = None) -> Iterator[Mark]:
        """Iterate over all markers of the node.

        :param name: If given, filter the results by the name attribute.
        :returns: An iterator of the markers of the node.
        """
        return (x[1] for x in self.iter_markers_with_node(name=name))

    def iter_markers_with_node(
        self, name: str | None = None
    ) -> Iterator[tuple[Node, Mark]]:
        """Iterate over all markers of the node.

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