HumanSignal/label-studio · error · ValidationError

sample() does not accept arguments.

Error message

sample() does not accept arguments.

What it means

The DataManager 'sample' expression generates random row values for an add/update-column action. It is deliberately argument-free: sample() fills the new column with random values drawn from range(0, size). Passing any arguments to sample() raises this ValidationError in add_expression before any tasks are processed.

Source

Thrown at label_studio/data_manager/actions/data_columns.py:294

    command, args = value.split('(', 1)
    if not command:
        raise ValidationError({'value': 'Expression command is required.'})
    args = process_arrays(args)
    args = args.replace(')', '').split(',')
    args = [] if len(args) == 1 and args[0] == '' else args
    for i, arg in enumerate(args):
        args[i] = arg.replace(';', ',').replace("'", '"')

    sample_values = None

    if command == 'range':
        if len(args) != 1:
            raise ValidationError({'value': 'range(start:int) requires one start argument.'})
        start = int(args[0])

    elif command == 'sample':
        if args:
            raise ValidationError({'value': 'sample() does not accept arguments.'})
        sample_values = iter(random.sample(range(0, size), size))

    elif command == 'random':
        if len(args) != 2:
            raise ValidationError({'value': 'random(min, max) requires two arguments.'})
        minimum, maximum = int(args[0]), int(args[1])

    elif command == 'choices':
        if not 0 < len(args) < 3:
            raise ValidationError({'value': 'choices(values:list, weights:list) requires one or two arguments.'})
        weights = json.loads(args[1]) if len(args) == 2 else None
        choices = json.loads(args[0])

    elif command == 'replace':
        if len(args) != 2:
            raise ValidationError({'value': 'replace(old_value, new_value) requires two arguments.'})
        old_value, new_value = json.loads(args[0]), json.loads(args[1])

View on GitHub (pinned to 0b49e9b539)

Solutions

1. Remove all entries from the args array so the sample expression payload has "args": []
2. If you intended bounded random values, use the random command with exactly two args: random(min, max)
3. If you intended sequential values, use range(start) with one argument

Example fix

// before
{"command": "sample", "args": ["100"]}
// after
{"command": "sample", "args": []}

if (expr.command === 'sample' && Array.isArray(expr.args) && expr.args.length > 0) {
  throw new Error('sample() takes no arguments');
}

function isValidSample(e) { return e.command === 'sample' && (!e.args || e.args.length === 0); }

try {
  await dm.addAction({id: 'add_data_field', expression: expr});
} catch (e) {
  if (String(e).includes('sample() does not accept arguments')) fixArgs(expr);
  else throw e;
}

When it happens

Trigger: Calling the add-data-field action with expression {"command": "sample", "args": ["100"]} or any non-empty args list; POSTing the mutation payload via _stage_column_mutation / _apply_column_mutation with extra parameters after the sample command.

Common situations: Developers confuse sample() with random(min, max) or range(start) and pass a count argument expecting sample(n); copy-pasted payloads from other commands; UI clients that always serialize an args array.

Related errors

• random(min, max) requires two arguments.
• choices(values:list, weights:list) requires one or two argum
• replace(old_value, new_value) requires two arguments.
• Undefined expression, you can use: {add_data_field_examples}
• Can't find '{action_id}' in registered actions

AI-assisted analysis of HumanSignal/label-studio@0b49e9b539 (2026-08-29). Data as JSON: /api/errors/2d79511af5d0e46f. Report an issue: GitHub.