Dear all

I have an issue I am trying to solve but I do not find a reasonable way. 

My game has 2 players per group with 2 roles ("seller" and "buyer"). Groups are shuffled randomly every round keeping the roles constant for 7 rounds in total.

For each seller I want to give a product from a list of 7 products and by the end of the 7 rounds the products are over. 
The buyer matched with the seller in the same round has the same product as the (matched) seller. 
Crucially, I want the buyer to see only ONCE each of the 7 products. 

The problem arises from the shuffling. By shuffling groups, some buyers are matched with a seller who has a product that the buyer has already seen. And this is of course wrong. 

I am considering this strategy:
    - in round = 1 
        I randomly draw from a list of available products for the seller
        I copy this random draw for the buyer
        I create a list of products drawn for the seller
        I create a list of products associated with the buyer
    - in round = 2 
        I need to match sellers and buyers conditional on the available products of both.

This second part is very complex. Do you have any suggestions?
I am also considering using dictionaries and group matrices to avoid this mechanism.



This is my starting code that gives a seller a product for each round:

    all_products = ['Product1', 'Product2', 'Product3', 'Product4', 'Product5', 'Product6']
    for player in subsession.get_players():
        participant = player.participant
        if player.role == "Seller":
            if subsession.round_number == 1:
                product = 'Product0'
                available_products = all_products
            else:
                round_number = subsession.round_number
                removed_products = participant.vars.get('removed_products', [])
                # Create a list of available products excluding removed products
                available_products = [x for x in all_products if x not in removed_products]
                if available_products:
                    product = random.choice(available_products)
                    removed_products.append(product)
                    participant.vars['removed_products'] = removed_products
                else:
                    product = 'No product available'

             player.product_this_round = product