D4Vinci/Scrapling · error · RuntimeError

No sessions registered

Error message

No sessions registered

What it means

The default_session_id property raises RuntimeError when no session has ever been registered. The manager promotes the first added session to default automatically, so hitting this means the SessionManager is empty — typically the spider started making requests before any session was configured.

Source

Thrown at scrapling/spiders/session.py:70

        :param session_id: ID of session to remove
        """
        if session_id not in self._sessions:
            raise KeyError(f"Session '{session_id}' not found")

        session = self._sessions.pop(session_id)
        if session_id in self._lazy_sessions:
            self._lazy_sessions.remove(session_id)

        if session and self._default_session_id == session_id:
            self._default_session_id = next(iter(self._sessions), None)

        return session

    @property
    def default_session_id(self) -> str:
        if self._default_session_id is None:
            raise RuntimeError("No sessions registered")
        return self._default_session_id

    @property
    def session_ids(self) -> list[str]:
        return list(self._sessions.keys())

    def get(self, session_id: str) -> Session:
        if session_id not in self._sessions:
            available = ", ".join(self._sessions.keys())
            raise KeyError(f"Session '{session_id}' not found. Available: {available}")
        return self._sessions[session_id]

    async def start(self) -> None:
        """Start all sessions that aren't already alive."""
        if self._started:
            return

        for sid, session in self._sessions.items():

View on GitHub (pinned to 5d213a2d47)

Solutions

1. Register at least one session during spider init: manager.add('default', my_session, default=True).
2. If sessions can be removed at runtime, re-register a fallback before popping the last one.
3. Make session-creation config unconditional or fail loudly at startup if the list is empty.

Example fix

# before
manager = SessionManager()
print(manager.default_session_id)  # RuntimeError

# after
manager.add('main', session, default=True)
print(manager.default_session_id)  # 'main'

if not manager.session_ids:
    manager.add('default', Session(), default=True)

assert manager.session_ids, 'no sessions configured before crawl start'

try:
    sid = manager.default_session_id
except RuntimeError:
    raise SystemExit('Configure at least one session before starting the spider')

When it happens

Trigger: Accessing manager.default_session_id, or issuing a request without an explicit session, on a SessionManager where add() was never called (or every session was popped).

Common situations: Forgetting to configure sessions in spider setup; popping the last session during dynamic reconfiguration while requests are still in flight; constructor code that adds sessions conditionally and the condition was false.

Related errors

• Can't use `adaptive` features while it's disabled globally,
• Session '{session_id}' already registered
• Session '{session_id}' not found. Available: {available}
• Session type {type(client)} not supported for async fetch
• No session found with the request session id

AI-assisted analysis of D4Vinci/Scrapling@5d213a2d47 (2026-08-14). Data as JSON: /api/errors/b55d6f3ac77e2207. Report an issue: GitHub.