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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _use_absolute_file_name(self, img):
 """ Change relative filename to abosolute file name. """

        img['file_name'] = os.path.join(
            self._imgdir, img['file_name'])
        assert os.path.isfile(img['file_name']), img['file_name']