Average of integers + recursion

cool_test.py

def average_integers(filename, recursion=False):
    integers_count = 0

    with open(filename.strip(), 'r') as reader:
        lines = reader.readlines()
        sum = 0
        for line in lines:
            try:
                sum += int(line)
                integers_count = integers_count + 1
            except ValueError:
                sum_file, integers_count_file = average_integers(line, recursion=True)
                sum += sum_file
                integers_count += integers_count_file

        if recursion:
            return sum, integers_count

        average = sum / integers_count
        return average


if __name__ == '__main__':
    average = average_integers(filename="integers.txt")
    print(average)