tracel-ai/burn · error

Invalid split specified {split}

Error message

Invalid split specified {split}

What it means

Input-validation guard in MNIST dataset download: the `split` argument must be exactly "train" or "test"; the match arms download the corresponding file set and the fallback panics with the offending value. It fires when a caller passes any other split name (typo, casing, or an unsupported split) to `MnistDataset::download`.

Source

Thrown at crates/burn-dataset/src/vision/mnist.rs:141

            .expect("Could not get cache directory")
            .join("burn-dataset");
        let split_dir = cache_dir.join("mnist").join(split);

        if !split_dir.exists() {
            create_dir_all(&split_dir).expect("Failed to create base directory");
        }

        // Download split files
        match split {
            "train" => {
                MnistDataset::download_file(TRAIN_IMAGES, &split_dir);
                MnistDataset::download_file(TRAIN_LABELS, &split_dir);
            }
            "test" => {
                MnistDataset::download_file(TEST_IMAGES, &split_dir);
                MnistDataset::download_file(TEST_LABELS, &split_dir);
            }
            _ => panic!("Invalid split specified {split}"),
        };

        split_dir
    }

    /// Download a file from the MNIST dataset URL to the destination directory.
    /// File download progress is reported with the help of a [progress bar](indicatif).
    fn download_file<P: AsRef<Path>>(name: &str, dest_dir: &P) -> PathBuf {
        // Output file name
        let file_name = dest_dir.as_ref().join(name);

        if !file_name.exists() {
            // Download gzip file
            let bytes = download_file_as_bytes(&format!("{URL}{name}.gz"), name);

            // Create file to write the downloaded content to
            let mut output_file = File::create(&file_name).unwrap();

View on GitHub (pinned to d16f7ba2ed)

Solutions

1. Pass `"train"` or `"test"` as the split, matching case exactly.
2. Normalize/validate the split string before calling the dataset constructor.
3. If a new split is required, add a match arm with the corresponding file URLs.

When it happens

Trigger: Thrown at crates/burn-dataset/src/vision/mnist.rs:141 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of tracel-ai/burn@d16f7ba2ed (2026-09-05). Data as JSON: /api/errors/ec2bab6504ebb7f5. Report an issue: GitHub.