pytest-dev/pytest · error · TypeError

session or parent must be provided

Error message

session or parent must be provided

What it means

Raised by Node.__init__ when neither session nor parent is supplied. Mirroring the config check, lines 172-177 fall back to parent.session when session is None; absent both, the node has no session to anchor its hook proxy and nodeid, so construction is rejected. The session is load-bearing for ihook dispatch and test lifecycle.

Solutions

1. Use Node.from_parent(parent, **kw) so session is inherited from parent.
2. Pass an explicit session object when constructing standalone.
3. Ensure a parent node is always provided in the construction chain.

Example fix

// before
node = MyItem(name='x')
// after
node = MyItem.from_parent(parent=collector, name='x')

assert session is not None or parent is not None, 'session or parent required'

def _node_has_session_source(session, parent) -> bool:
    return session is not None or parent is not None

When it happens

Trigger: Node(...) with session=None and parent=None; constructing a node detached from the Session, e.g. in a unit test or a buggy plugin that bypasses from_parent.

Common situations: Plugin authors building nodes manually without a parent; mocking frameworks that construct nodes without a session fixture.

Related errors

• 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
• expected string as 'msg' parameter, got ' '…

AI-assisted analysis of pytest-dev/pytest@0d6fbdeffa (2026-08-11). Data as JSON: /api/errors/d2ccbefe110661f1. Report an issue: GitHub.

Appendix: source

Thrown at src/_pytest/nodes.py:176

        self.name: str = name

        #: The parent collector node.
        self.parent = parent

        if config:
            #: The pytest config object.
            self.config: Config = config
        else:
            if not parent:
                raise TypeError("config or parent must be provided")
            self.config = parent.config

        if session:
            #: The pytest session this node is part of.
            self.session: Session = session
        else:
            if not parent:
                raise TypeError("session or parent must be provided")
            self.session = parent.session

        if path is None:
            assert parent is not None
            path = parent.path
        #: Filesystem path where this node was collected from.
        self.path: pathlib.Path = path

        # The explicit annotation is to avoid publicly exposing NodeKeywords.
        #: Keywords/markers collected from all scopes.
        self.keywords: MutableMapping[str, Any] = NodeKeywords(self)

        #: The marker objects belonging to this node.
        self.own_markers: list[Mark] = []

        #: Allow adding of extra keywords to use for matching.
        self.extra_keyword_matches: set[str] = set()

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