code: def _get_key_alias_from_cache(self, key_arn):
          '''
          Find a key's alias by looking up its key_arn in the KEY_METADATA
          cache. This function will only work after a key has been lookedup by
          its alias and is meant as a convenience function for turning an ARN
          that's already been looked up back into its alias.
          '''
          for alias in self.KEY_METADATA:
              if self.KEY_METADATA[alias]['KeyMetadata']['Arn'] == key_arn:
                  return alias
          return Nonf _get_key_alias_from_cache(self, key_arn):
          '''
          Find a key's alias by looking up its key_arn in the KEY_METADATA
          cache. This function will only work after a key has been lookedup by
          its alias and is meant as a convenience function for turning an ARN
          that's already been looked up back into its alias.
          '''
          for alias in self.KEY_METADATA:
              if self.KEY_METADATA[alias]['KeyMetadata']['Arn'] == key_arn:
                  return alias
          return None
docs: Find a key's alias by looking up its key_arn in the KEY_METADATA
          cache. This function will only work after a key has been lookedup by
          its alias and is meant as a convenience function for turning an ARN
          that's already been looked up back into its alias.