SeleniumHQ/selenium · error · ValueError

Event '{event}' not found. Available events: {self._availabl

Error message

Event '{event}' not found. Available events: {self._available_events}

What it means

Raised as a ValueError by _EventManager.validate_event() when the event name passed to it is not a key in the event_configs dictionary. The manager holds a registry of supported events (built from EventConfig entries) and computes _available_events as a sorted, comma-joined string for the error message. Calling validate_event with an unregistered event name is a usage error indicating the event is not part of this BiDi module's supported event set.

Source

Thrown at py/private/_event_manager.py:109

    def __init__(self, conn, event_configs: dict[str, EventConfig]):
        self.conn = conn
        self.event_configs = event_configs
        self.subscriptions: dict = {}
        self._event_wrappers = {}  # Cache of _EventWrapper objects
        self._bidi_to_class = {config.bidi_event: config.event_class for config in event_configs.values()}
        self._available_events = ", ".join(sorted(event_configs.keys()))
        self._subscription_lock = threading.Lock()

        # Create event wrappers for each event
        for config in event_configs.values():
            wrapper = _EventWrapper(config.bidi_event, config.event_class)
            self._event_wrappers[config.bidi_event] = wrapper

    def validate_event(self, event: str) -> EventConfig:
        event_config = self.event_configs.get(event)
        if not event_config:
            raise ValueError(f"Event '{event}' not found. Available events: {self._available_events}")
        return event_config

    def subscribe_to_event(self, bidi_event: str, contexts: list[str] | None = None) -> None:
        """Subscribe to a BiDi event if not already subscribed."""
        with self._subscription_lock:
            if bidi_event not in self.subscriptions:
                session = Session(self.conn)
                result = session.subscribe([bidi_event], contexts=contexts)
                sub_id = result.get("subscription") if isinstance(result, dict) else None
                self.subscriptions[bidi_event] = {
                    "callbacks": [],
                    "subscription_id": sub_id,
                }

    def unsubscribe_from_event(self, bidi_event: str) -> None:
        """Unsubscribe from a BiDi event if no more callbacks exist."""
        with self._subscription_lock:
            entry = self.subscriptions.get(bidi_event)

View on GitHub (pinned to aa36b38e69)

Solutions

Read the 'Available events' portion of the error message — it lists the exact valid event names for this module.
Copy the exact event name string from the available events list into your code to avoid spelling or casing mismatches.
Confirm you are calling the method on the correct BiDi module (e.g. network events on the network module, log events on the log module).
Check the Selenium version's API docs for renamed or newly added events if upgrading.

Example fix

# before
manager.validate_event('responceStarted')  # typo

# after
manager.validate_event('responseStarted')  # from available events list

Defensive patterns

Strategy: validation

Validate before calling

# Validate before calling
valid_events = set(manager.event_configs.keys())
if event_name not in valid_events:
    raise ValueError(f'Use one of: {sorted(valid_events)}')
manager.validate_event(event_name)

Try / catch

try:
    manager.validate_event(event_name)
except ValueError as e:
    if 'not found' in str(e):
        # read available events from the message and correct
        pass
    else:
        raise

Prevention

Read the Available events list from the error message for valid names.
Use constants or enums for event names rather than string literals to avoid typos.
Confirm the event belongs to the correct BiDi module.

When it happens

Trigger: Calling an event-validation entry point (e.g. add_event_listener or callback registration on a generated BiDi module) with an event string that does not match any key in that module's event_configs. The message includes the sorted list of valid event names for diagnostics.

Common situations: Misspelling an event name (e.g. 'responceStarted' instead of 'responseStarted'); using an event name from a different BiDi module than the one being called; version mismatch where an event was renamed in a newer Selenium release; mixing up camelCase vs snake_case event identifiers.

Related errors

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/977affd2e0caf3f9. Report an issue: GitHub.