Convert the `ETags` object into a python set.  Per default all the
        weak etags are not part of this set.

def as_set(self, include_weak=False):
        """Convert the `ETags` object into a python set.  Per default all the
        weak etags are not part of this set."""
        rv = set(self._strong)
        if include_weak:
            rv.update(self._weak)
        return rv