code: def with_cache_loader(self, func, only_read=False):
          
          self.logger.info('Enabled cache loader %s' % get_function_signature(func))
          self.cache_loader = func
          return True
docs: >>> cache = Cache(log_level=logging.WARNING)
          >>> def cache_loader(key): pass
          >>> cache.with_cache_loader(cache_loader)
          True
          >>> def cache_loader_b(key, value): pass
          >>> cache.with_cache_loader(cache_loader_b)
          False