Storing calculated values in an object

Question

Recently I\'ve been writing a bunch of code like this:

class A:
  def __init__(self, x):
    self.x = x
    self._y = None

  def y(self):
    if self._y is          


        

Answer 1

My EAFP pythonista approach is described by the following snippet.

My classes inherit _reset_attributes from WithAttributes and use it to invalidate the scary values.

class WithAttributes:

    def _reset_attributes(self, attributes):
        assert isinstance(attributes,list)
        for attribute in attributes:
            try:
                delattr(self, '_' + attribute)
            except:
                pass

class Square(WithAttributes):

    def __init__(self, size):
        self._size = size

    @property
    def area(self):
        try:
            return self._area
        except AttributeError:
            self._area = self.size * self.size
            return self._area

    @property
    def size(self):
        return self._size

    @size.setter
    def size(self, size):
        self._size = size
        self._reset_attributes('area')