Python Flask WTForms ensure uniqueness of a field
You can write your own validator and use it as you wish.
I am using flask with WTForms to create online form. In this form I have a section where user has 10 dropdown menus (with same content; they need to rank items). I'd like to ensure that the same item is not selected multiple times. However, I can't find a way to do so. In WTForms there is a validator Equals() which checks if the field equals to another field, but no such validator to check if it does not equal. 
Any help would be appreciated.