gistfile1.txt

import csv

with open('other_list.txt', 'r') as other_list:
    sublist_something = other_list.readlines()

complete_list = {}
with open('master_list.txt', 'r') as master_list:
    for account_id in master_list.readlines():
        complet_list[account_id] = {}
        if account_id in sublist_something:
            complete_list[account_id]['value_i_care_about'] = True
        else:
            complete_list[account_id]['value_i_care_about'] = False