rohitg00/ai-engineering-from-scratch · error · IndexError

window index {index} out of range

Error message

window index {index} out of range

What it means

Error "window index {index} out of range" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at phases/19-capstone-projects/31-tokenized-dataset-sliding-window/code/main.py:190

        self.ids = torch.tensor(ids, dtype=torch.long)
        self.context_length = context_length
        self.stride = stride

    @staticmethod
    def count_windows(num_ids: int, context_length: int, stride: int) -> int:
        usable = num_ids - (context_length + 1)
        if usable < 0:
            return 0
        return 1 + usable // stride

    def __len__(self) -> int:
        return self.count_windows(self.ids.numel(), self.context_length, self.stride)

    def __getitem__(self, index: int) -> tuple[torch.Tensor, torch.Tensor]:
        if index < 0:
            index += len(self)
        if index < 0 or index >= len(self):
            raise IndexError(f"window index {index} out of range")
        start = index * self.stride
        end = start + self.context_length + 1
        window = self.ids[start:end]
        return window[:-1].clone(), window[1:].clone()


def make_dataloader(
    dataset: SlidingWindowDataset,
    batch_size: int,
    shuffle: bool = True,
    base_seed: int = 0,
    epoch: int = 0,
    drop_last: bool = True,
) -> DataLoader:
    """Build a DataLoader with a deterministic per-epoch shuffle."""
    generator = torch.Generator()
    generator.manual_seed(base_seed + epoch)
    return DataLoader(

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at phases/19-capstone-projects/31-tokenized-dataset-sliding-window/code/main.py:190 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/0fb213e569d14a22. Report an issue: GitHub.