Wtforms - How FieldList receives input from frontend

Question

I am curious how FieldList of wtforms works, I did some experiment with the front end using javascript.

So basically I have a multiple repeatable fields, and there is a button to dynamically add new field and changes its id, name, for following the wtforms convention (e.g. transaction-item-0-something for first field, transaction-item-1-something for second field, etc).

One experiment that I did was putting same id and name same for 2 of field list (e.g. transaction-item-0-something for 1st field, transaction-item-0-something for 2nd field). and wtforms only took the first input value (is expected).

Second experiment was the one that bugs me, I deliberately changed some of the number so it would skip some number (transaction-item-0-something for 1st field, transaction-item-2-something for 2nd field), and it worked fine, wtforms received both of the input.

So this makes me wondering, do id and name not need to be ordered? if so how the wtforms handle the received input then, is just getting the all the ids of item which contains transaction-item-x-something? and just loop through it but also check if the registered id is in there?

Answer 1

Actually, I just dug through the source code and found out the order does not matter, as long as it is a number (.isdigit()), it will loop through all the received data and then put it inside a set which is like python keys in dictionary, so duplicate value will be removed.

Which means html will send every <input> regardless of its id or name is same and let the backend handles it