An example of python attributes, properties, and descriptors. This is the full code from this blog post: https://bradmontgomery.net/blog/2013/09/12/attribute-any-other-name/

attributes.py

"""
An example of python's attributes, properties, __getattr__, and Descriptors.
See the ``N`` class below.

For a full description, see this blog post:
https://bradmontgomery.net/blog/2013/09/12/attribute-any-other-name/

"""

def is_prime(number):
    """Determine if a number is prime. Shamelessly taken from:
    http://stackoverflow.com/a/4117879/182778

    Returns True or False
    """
    return number > 1 and all(number % i for i in xrange(2, number))


class PrimeNumbers(object):
    """This class implements a descriptor (ie. a property or attribute) that
    will only store Prime Numbers. The class on which it is attached must have
    a ``numbers`` attribute."""

    def filter_primes(self, numbers):
        """Use the ``is_prime`` function to pluck only primes from a list of
        numbers."""
        return filter(is_prime, numbers)

    def __get__(self, instance, owner):
        """Get only the prime numbers from the ``numbers`` attribute on the
        ``instance`` object (an N object).

        Note:
            * ``instance`` will be an instance of our N class.
            * ``owner`` will be a reference to the N class (not an instance
              of it)

        """
        return self.filter_primes(instance.numbers)

    def __set__(self, instance, values):
        """Set the value of ``instance.numbers``, but *only* store primes.
        ``values`` is just a list of numbers.
        """
        instance.numbers = self.filter_primes(values)


class N(object):
    """A simple class illustrating ways to access an "attribute"."""
    numbers = range(10)
    prime_numbers = PrimeNumbers()

    @property
    def even_numbers(self):
        return [num for num in self.numbers if num % 2 == 0]

    @even_numbers.setter
    def even_numbers(self, values):
        # Just pass any values on to the ``numbers`` attribute
        self.numbers = values

    def __getattr__(self, name):
        if name == "odd_numbers":
            return [num for num in self.numbers if num % 2 != 0]

        # Raise an AttributeError, for all other attribute names.
        raise AttributeError("'N' object has no attribute '{0}'".format(name))