code: def amazon_s3_url(self, sat, band):
          
          if band != 'MTL':
              filename = '%s_B%s.TIF' % (sat['scene'], band)
          else:
              filename = '%s_%s.txt' % (sat['scene'], band)
  
          return url_builder([self.s3, sat['sat'], sat['path'], sat['row'], sat['scene'], filename])
docs: Return an amazon s3 url the contains the scene and band provided.
  
          :param sat:
              Expects an object created by scene_interpreter method
          :type sat:
              dict
          :param filename:
              The filename that has to be downloaded from Amazon
          :type filename:
              String
  
          :returns:
              (String) The URL to a S3 file