code: def as_node(cls, obj):
          
          if isinstance(obj, cls):
              return obj
          elif is_string(obj):
              # Assume filepath.
              return FileNode(obj)
          elif obj is None:
              return obj
          else:
              raise TypeError("Don't know how to convert %s to Node instance." % obj)
docs: Convert obj into a Node instance.
  
          Return:
              obj if obj is a Node instance,
              cast obj to :class:`FileNode` instance of obj is a string.
              None if obj is None