part2.py

def identify_fields(possible_field_pos):
    def gen(b):
        if len(b) == len(possible_field_pos):
            return True

        for item in possible_field_pos[len(b)][1]:
            if item not in (item for i, item in b):
                b.append((possible_field_pos[len(b)][0], item))
                if gen(b) is not None:
                    return b
                b.pop()

    return gen([])


with open("input.txt") as file:
    line = file.readline().strip()

    # Making dictionaty of fields:
    fields = {}
    while line:
        fields[line.split(':')[0]] = [list(map(int, range_.split('-'))) for range_ in line.split(':')[1].split("or")]
        line = file.readline().strip()

    # Reading my ticket
    file.readline()
    my_ticket = list(map(int, file.readline().split(',')))
    file.readline()
    file.readline()
    line = file.readline().strip()

    # Determining valid nearby tickets
    valid_tickets = []
    while line:
        ticket = list(map(int, line.split(',')))

        for value in ticket:
            if not any(
                any(left <= value <= right for left, right in range_)
                for range_ in fields.values()
            ):
                break

        else:
            valid_tickets.append(ticket)

        line = file.readline().strip()

possible_field_pos = [[] for _ in range(len(my_ticket))]

for field_index in range(len(my_ticket)):
    for field, range_ in fields.items():
        if all(
            any(left <= ticket[field_index] <= right for left, right in range_)
            for ticket in valid_tickets
        ):
            possible_field_pos[field_index].append(field)

possible_field_pos = sorted((
    (i, possible_fields) for i, possible_fields in enumerate(possible_field_pos)
), key=lambda x: len(x[1]))

answer = 1
for i, field in identify_fields(possible_field_pos):
    if field.startswith("departure"):
        answer *= my_ticket[i]

print(answer)