code: def get(cls, rkey):
          
  
          if rkey in cls._cached:
              logger.info('Resource %s is in cache.' % rkey)
              return cls._cached[rkey]
          if rkey in cls._stock:
              img = cls._load_image(rkey)
              return img
          else:
              raise StockImageException('StockImage: %s not registered.' % rkey)
docs: Get image previously registered with key rkey.
          If key not exist, raise StockImageException