Python merge lists of dicts by key:value pair

Question

l1 = [{\'item_id\': 3, \'customer_id\': 3}, {\'item_id\': 4, \'customer_id\': 1}, {\'item_id\': 5, \'customer_id\': 3}, {\'item_id\': 6, \'customer_id\': 3,}]

l2 = [{