from math import sqrt

​

def is_perfect(num):

    """

    This function checks if num is a perfect number.

    Note that a number is said to be perfect if it 

    matches the sum of all of its divisors, excluding

    itself.

​

    For example:  6 = 1 + 2 + 3, 28 = 1 + 2 + 4 + 7 + 14, 

    and 496 = 1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 + 248, 

    are all perfect numbers.

​

    Time complexity: O(sqrt(n)), with sqrt being square root

    Space complexity: O(1)

    """

    if num <= 5:

        return False

    sum = 1

    div = 2

    upper = sqrt(num)

    while div <= upper:

        if num % div == 0:

            sum = sum + div + num // div

        div += 1

    return (num == sum)

​

print("All perfect numbers below 100: ")

for n in range(100):

    """

    The below prints:

    6

    28

    """

    if is_perfect(n):

        print(n)

​