@property
def arr(self):
    if (self._arr is not None):
        return self._arr
    self._arr = functools.partial(YTArray, registry=self.unit_registry)
    return self._arr
@property
def arr(self):
    if (self._arr is not None):
        return self._arr
    self._arr = functools.partial(YTArray, registry=self.unit_registry)
    return self._arr