Exercise: Perfect Number |2|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Perfect numbers from
`Wikipedia <https://en.wikipedia.org/wiki/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
instance, 6 has divisors 1, 2 and 3 (excluding itself), and 1 + 2 + 3 =
6, so 6 is a perfect number.”

Write a function named *is_perfect*, takes an integer and returns True
if the given integer is perfect, and False otherwise.

*Hint:* You can define a helper function to decide a number is divisor
of another number.

.. container:: sampleio

   Sample I/O:

.. |2| image:: ../../figures/difficulty_four.png
   :class: difficulty

.. code:: default

   >>> is_perfect(6)
   True
   >>> is_perfect(7)
   False
   >>> is_perfect(28)
   True
   >>> is_perfect(30)
   False