How to create a schema that has no

Given the following schema:

class CalendarSchema(Schema):
    days_of_month = fields.List(fields.Integer(), default=[], validate=validate.ContainsOnly(range(1, 31 + 1)))

The above schema works fine as long as the array passed contains the value between [1, 31]. However, if the array was an empty array ([]), the validation fails. How can I tweak fields.List such that it accepts an empty array?

[sloria]

After giving this some thought, I think ContainsOnly should accept empty values as valid inputs. Validating against empty vs. non-empty is outside the responsibility of ContainsOnly. If you need to validate that input is non-empty, use Length(min=1).

[YuriHeupa]

Would be nice to have ContainsOnly accepting a param like allow_empty to make empty lists allowed