Python summing values in list if it exists in another list

Question

I have a list and a set:

a_list = [[\'1\', 2], [\'2\', 1], [\'1\', 1]]

b_list = {\'1\', \'2\'}

I\'m looking to correspond the items in b_list

Answer 1

This returns sums only for items defined in find.

items = [['1', 2], ['2', 1], ['1', 1], ['3',1]]
find = {'1', '2'}
results = {}

for item in items:
    key = item[0]
    value = item[1]
    if key in find:
        results[key] = results.get(key,0) + value

[[key, value] for key, value in results.items()] 

Outputs [['2', 1], ['1', 3]]