Initially sets up an attribute.

def _set_attr(self, name, doc=None, preload=False):
        "Initially sets up an attribute."

        if doc is None:
            doc = 'The {name} attribute.'.format(name=name)

        if not hasattr(self._attr_func_, name):
            attr_prop = property(
                functools.partial(self._setable_get_, name),
                functools.partial(self._setable_set_, name),
                doc=doc
            )

        elif preload:
            func = getattr(self._attr_func_, name)
            setattr(self._attr_data_, name, func())
            delattr(self._attr_func_, name)
            attr_prop = property(
                functools.partial(self._simple_get_, name),
                doc=doc
            )

        else:
            attr_prop = property(
                functools.partial(self._loadable_get_, name),
                doc=doc
            )

        setattr(type(self), name, attr_prop)