code: def mkdir(self, children, mode=0o0755, return_node=True):
          
          result = None
  
          if isinstance(children, (str, unicode)):
              if os.path.isabs(children):
                  raise BadValueError('Cannot mkdir an absolute path: {path}'.format(path=self._pyerarchy_path))
  
              rel_path = os.path.join(self._pyerarchy_path, children)
              os.makedirs(rel_path, mode)
  
              if return_node:
                  result = Node(rel_path)
          else:
              for child in children:
                  self.mkdir(child, mode, False)
  
          return result
docs: Creates child entities in directory.
  
          Raises exception if the object is a file.
  
          :param children: The list of children to be created.
          :return: The child object, if one child is provided. None, otherwise.