HumanSignal/label-studio · error · ValidationError

range(start:int) requires one start argument.

Error message

range(start:int) requires one start argument.

What it means

For the 'range' command, add_expression enforces exactly one argument: range(start:int). Supplying zero or multiple arguments raises ValidationError {'value': 'range(start:int) requires one start argument.'}.

Source

Thrown at label_studio/data_manager/actions/data_columns.py:289

def add_expression(queryset, size, value, value_name):
    if '(' not in value or not value.endswith(')'):
        raise ValidationError({'value': 'Expression must use the form command(arguments).'})
    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])

View on GitHub (pinned to 0b49e9b539)

Solutions

1. Pass exactly one integer argument: 'range(N)' generates a sequence based on task index starting at N.
2. Remove extra arguments or switch to a different command if a start/stop range is needed.
3. Cast arguments to int in the payload (they are parsed with int(args[0])).

Example fix

// before
value = 'range(1, 10)'
// after
value = 'range(1)'

args_part = value[value.index('(')+1:-1].strip()
if value.startswith('range'):
    assert len([a for a in args_part.split(',') if a.strip()]) == 1, 'range takes exactly one int argument'

import re
def is_valid_range_expression(value):
    return isinstance(value, str) and re.fullmatch(r'range\(\s*-?\d+\s*\)', value) is not None

from rest_framework.exceptions import ValidationError
try:
    add_data_field(project, qs, request=request)
except ValidationError as e:
    if 'requires one start argument' in str(e):
        fix_to_single_arg_expression()

When it happens

Trigger: Submitting Expression 'range()' (no args), 'range(1, 10)' or 'range(1;10)' (two args — note ';' is converted to ',' before this check), or 'range( 5 , 6 )'.

Common situations: User assumes Python-like range(start, stop) semantics and passes two arguments; empty parentheses from the dialog template.

Related errors

• Expression must use the form command(arguments).
• Expression command is required.
• Choose a supported column type.
• Select an existing column or enter a new column name.
• Column name cannot contain {UNQUERYABLE_COLUMN_NAME_CHARACTE

AI-assisted analysis of HumanSignal/label-studio@0b49e9b539 (2026-08-29). Data as JSON: /api/errors/ca6dbceda1015705. Report an issue: GitHub.