code: def get_folder(self, *, folder_id=None, folder_name=None):
          
          if folder_id and folder_name:
              raise RuntimeError('Provide only one of the options')
  
          if not folder_id and not folder_name:
              raise RuntimeError('Provide one of the options')
  
          if folder_id:
              # get folder by it's id, independent of the parent of this folder_id
              url = self.build_url(
                  self._endpoints.get('get_folder').format(id=folder_id))
              params = None
          else:
              # get folder by name. Only looks up in child folders.
              if self.root:
                  url = self.build_url(self._endpoints.get('root_folders'))
              else:
                  url = self.build_url(
                      self._endpoints.get('child_folders').format(
                          id=self.folder_id))
              params = {'$filter': "{} eq '{}'".format(self._cc('displayName'),
                                                       folder_name), '$top': 1}
  
          response = self.con.get(url, params=params)
          if not response:
              return None
  
          if folder_id:
              folder = response.json()
          else:
              folder = response.json().get('value')
              folder = folder[0] if folder else None
              if folder is None:
                  return None
  
          self_class = getattr(self, 'folder_constructor', type(self))
          # Everything received from cloud must be passed as self._cloud_data_key
          # We don't pass parent, as this folder may not be a child of self.
          return self_class(con=self.con, protocol=self.protocol,
                            main_resource=self.main_resource,
                            **{self._cloud_data_key: folder})
docs: Get a folder by it's id or name
  
          :param str folder_id: the folder_id to be retrieved.
           Can be any folder Id (child or not)
          :param str folder_name: the folder name to be retrieved.
           Must be a child of this folder.
          :return: a single folder
          :rtype: mailbox.Folder or None