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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 _get_bandfilenames(self):
 """Get the instrument rsr filenames"""

        for band in self.bandnames:
            LOG.debug("Band = %s", str(band))
            self.filenames[band] = os.path.join(self.path,
                                                self.options[self.platform_name + '-' +
                                                             self.instrument][band])
            LOG.debug(self.filenames[band])
            if not os.path.exists(self.filenames[band]):
                LOG.warning("Couldn't find an existing file for this band: %s",
                            str(self.filenames[band]))