HumanSignal/label-studio · warning · ValueError

Response is not list: {payload}

Error message

Response is not list: {payload}

What it means

AllImportStorageListAPI._get_response proxies a per-storage-type list view and expects response.data to be a list. If the DRF view returns a non-list payload (object, dict, paginated response), it raises ValueError — but the method catches all exceptions, logs 'Can't process ...', and returns [] so that the aggregated sum() of lists still works.

Source

Thrown at label_studio/io_storages/all_api.py:144

        extensions={
            'x-fern-sdk-group-name': ['import_storage'],
            'x-fern-sdk-method-name': 'list',
            'x-fern-audiences': ['internal'],
        },
    ),
)
class AllImportStorageListAPI(generics.ListAPIView):
    queryset = S3ImportStorage.objects.none()
    parser_classes = (JSONParser, FormParser, MultiPartParser)
    permission_required = all_permissions.storages_view

    def _get_response(self, api, request, *args, **kwargs):
        try:
            view = api.as_view()
            response = view(request._request, *args, **kwargs)
            payload = response.data
            if not isinstance(payload, list):
                raise ValueError(f'Response is not list: {payload}')
            return payload
        except Exception:
            logger.error(f"Can't process {api.__class__.__name__}", exc_info=True)
            return []

    def list(self, request, *args, **kwargs):
        list_responses = sum(
            [self._get_response(s['import_list_api'], request, *args, **kwargs) for s in _common_storage_list], []
        )
        return Response(list_responses)


@method_decorator(
    name='get',
    decorator=extend_schema(
        tags=['Storage'],
        summary='List all export storages from the project',
        description='Retrieve a list of the export storages of all types with their IDs.',

View on GitHub (pinned to 0b49e9b539)

Solutions

1. Check the error log for "Can't process <ApiName>" to identify which storage API failed.
2. Ensure the storage type's list API returns a plain list (disable pagination or return .data list).
3. Fix the misconfigured storage backend (credentials/bucket) causing the inner view to fail.
4. Optionally make _get_response unwrap paginated objects ({'results': [...]}) before the isinstance check.

Example fix

// before
payload = response.data
if not isinstance(payload, list):
    raise ValueError(f'Response is not list: {payload}')
// after
payload = response.data
if isinstance(payload, dict) and 'results' in payload:
    payload = payload['results']
if not isinstance(payload, list):
    raise ValueError(f'Response is not list: {payload}')

resp = view(request._request, *args, **kwargs)
payload = resp.data.get('results') if isinstance(resp.data, dict) else resp.data
if not isinstance(payload, list):
    logger.warning('import storage list for %s returned non-list', api.__name__)

def is_list_payload(resp) -> bool:
    data = resp.data.get('results') if isinstance(resp.data, dict) else resp.data
    return isinstance(data, list)

try:
    payload = self._get_response(api, request, *args, **kwargs)
except ValueError:
    payload = []  # per-type isolation: one bad backend shouldn't break the aggregate

When it happens

Trigger: A storage type's import_list_api view returning a paginated/serialized object payload instead of a plain list, or raising before producing list data — typically when one storage backend is misconfigured.

Common situations: Adding a new storage type whose list API returns a dict; pagination enabled on the inner view changing response shape; credentials misconfigured for S3/GCS/Azure causing the inner view to error and fall into the catch-all.

Related errors

• "file_upload_ids" parameter must be a list of integers
• sample() does not accept arguments.
• random(min, max) requires two arguments.
• choices(values:list, weights:list) requires one or two argum
• replace(old_value, new_value) requires two arguments.

AI-assisted analysis of HumanSignal/label-studio@0b49e9b539 (2026-08-29). Data as JSON: /api/errors/c0b65203d9ce1526. Report an issue: GitHub.