"""
Read file into texts and calls.
It's ok if you don't understand how to read files.
"""
import csv

with open('texts.csv', 'r') as f:
    reader = csv.reader(f)
    texts = list(reader)

with open('calls.csv', 'r') as f:
    reader = csv.reader(f)
    calls = list(reader)

"""
TASK 4:
The telephone company want to identify numbers that might be doing
telephone marketing. Create a set of possible telemarketers:
these are numbers that make outgoing calls but never send texts,
receive texts or receive incoming calls.

Print a message:
"These numbers could be telemarketers: "
<list of numbers>
The list of numbers should be print out one per line in lexicographic order with no duplicates.
"""
def task_4(texts, calls):
    numbers_not_telemarketers = set()
    numbers_make_call = set()
    numbers_telemarketers = set()

    for text in texts:
        numbers_not_telemarketers.add(text[0])
        numbers_not_telemarketers.add(text[1])

    for call in calls:
        numbers_make_call.add(call[0])
        numbers_not_telemarketers.add(call[1])

    numbers_telemarketers = numbers_make_call.difference(numbers_not_telemarketers)

    return sorted(numbers_telemarketers)

numbers_telemarketers = task_4(texts, calls)
print("These numbers could be telemarketers:")
print(*numbers_telemarketers, sep='\n')
