microsoft/qlib · error · NotImplementedError

Subclass of CalendarStorage must implement `__len__` method

Error message

Subclass of CalendarStorage must implement `__len__`  method

What it means

Error "Subclass of CalendarStorage must implement `__len__` method" thrown in microsoft/qlib.

Source

Thrown at qlib/data/storage/storage.py:188

        ------
        ValueError
            If the data(storage) does not exist, raise ValueError

        """
        raise NotImplementedError(
            "Subclass of CalendarStorage must implement `__getitem__(i: int)`/`__getitem__(s: slice)`  method"
        )

    def __len__(self) -> int:
        """

        Raises
        ------
        ValueError
            If the data(storage) does not exist, raise ValueError

        """
        raise NotImplementedError("Subclass of CalendarStorage must implement `__len__`  method")


class InstrumentStorage(BaseStorage):
    def __init__(self, market: str, freq: str, **kwargs):
        self.market = market
        self.freq = freq
        self.kwargs = kwargs

    @property
    def data(self) -> Dict[InstKT, InstVT]:
        """get all data

        Raises
        ------
        ValueError
            If the data(storage) does not exist, raise ValueError
        """
        raise NotImplementedError("Subclass of InstrumentStorage must implement `data` method")

View on GitHub (pinned to 79633dd950)

Solutions

1. Implement the `__len__` method in your CalendarStorage subclass.
2. Use the built-in FileCalendarStorage which implements `__len__`.

When it happens

Trigger: This error is raised at qlib/data/storage/storage.py:188 when the guard condition fails: "Subclass of CalendarStorage must implement `__len__` method". It triggers when the code path receives input or a state that violates the precondition checked at this point — e.g. an unimplemented abstract method being called, an unsupported argument type/value, or an invalid configuration. To avoid it, satisfy the documented precondition before this call: implement the required method in your subclass, or pass a supported value of the expected type as described by the message.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/qlib@79633dd950 (2026-08-15). Data as JSON: /api/errors/0f084297ba630691. Report an issue: GitHub.