"""
== Perfect Number ==
In number theory, a perfect number is a positive integer that is equal to the sum of
its positive divisors, excluding the number itself.
For example: 6 ==> divisors[1, 2, 3, 6]
Excluding 6, the sum(divisors) is 1 + 2 + 3 = 6
So, 6 is a Perfect Number
Other examples of Perfect Numbers: 28, 486, ...
https://en.wikipedia.org/wiki/Perfect_number
"""
def perfect(number: int) -> bool:
"""
>>> perfect(27)
False
>>> perfect(28)
True
>>> perfect(29)
False
Start from 1 because dividing by 0 will raise ZeroDivisionError.
A number at most can be divisible by the half of the number except the number
itself. For example, 6 is at most can be divisible by 3 except by 6 itself.
"""
return sum(i for i in range(1, number // 2 + 1) if number % i == 0) == number
if __name__ == "__main__":
print("Program to check whether a number is a Perfect number or not...")
number = int(input("Enter number: ").strip())
print(f"{number} is {'' if perfect(number) else 'not '}a Perfect Number.")