def METHOD_NAME(self, siglum):
    if self._mobj:
        # If provided with a manuscript object, use that
        mobj = self._mobj
    elif siglum in self._manuscript_cache:
        mobj = self._manuscript_cache[siglum]
    else:
        mobj = Manuscript.objects.get(siglum=siglum)
        self._manuscript_cache[siglum] = mobj
    return mobj