product_qty = {}
for line in order.order_line: # assuming "order" is the parent record with a one2many field "order_line"
    if line.product_id.id in product_qty:
        product_qty[line.product_id.id] += line.product_uom_qty
    else:
        product_qty[line.product_id.id] = line.product_uom_qty

# Now, product_qty dictionary will contain product IDs as keys and their respective quantities as values