code: def set_data_dtype(self, dtype):
      self.arr = self.arr.astype(dtype)
  
imports: import warnings
  from itertools import product
  import numpy
  import pytest
  from ..filebasedimages import FileBasedHeader, FileBasedImage, SerializableImage
  from .test_image_api import GenericImageAPI, SerializeMixin
label_desc: Use image node_id 9 for calling the FBNumpyImage obj's underlying member method code with example usage: obj.set_data_dtype(dtype) without return types