class LazyProperty(object):
    """
    Decorator for easier creation of ``property`` from potentially expensive to
    calculate attribute of the class.

    Usage::

      class Foo(object):
          @LazyProperty
          def bar(self):
              print 'Calculating self._bar'
              return 42

    Taken from http://blog.pythonisito.com/2008/08/lazy-descriptors.html and
    used widely.
    """

    def __init__(self, func):
        self._func = func
        self.__name__ = func.__name__
        self.__doc__ = func.__doc__

    def __get__(self, obj, klass=None):
        if obj is None:
            return None
        result = obj.__dict__[self.__name__] = self._func(obj)
        return result