microsoft/qlib · error · NotImplementedError

Subclass of InstrumentStorage must implement `__len__` meth

Error message

Subclass of InstrumentStorage must implement `__len__`  method

What it means

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

Source

Thrown at qlib/data/storage/storage.py:252

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

    def __getitem__(self, k: InstKT) -> InstVT:
        """x.__getitem__(k) <==> x[k]"""
        raise NotImplementedError("Subclass of InstrumentStorage must implement `__getitem__` method")

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

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

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


class FeatureStorage(BaseStorage):
    def __init__(self, instrument: str, field: str, freq: str, **kwargs):
        self.instrument = instrument
        self.field = field
        self.freq = freq
        self.kwargs = kwargs

    @property
    def data(self) -> pd.Series:
        """get all data

        Notes
        ------
        if data(storage) does not exist, return empty pd.Series: `return pd.Series(dtype=np.float32)`
        """
        raise NotImplementedError("Subclass of FeatureStorage must implement `data` method")

View on GitHub (pinned to 79633dd950)

Solutions

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

When it happens

Trigger: This error is raised at qlib/data/storage/storage.py:252 when the guard condition fails: "Subclass of InstrumentStorage 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/e1a3ac3bb635b6a4. Report an issue: GitHub.