class_docstr: Base Dataset with directory checker.
  
  Parameters
  ----------
  root : str
      The root path of xxx.names, by default is '~/.mxnet/datasets/foo', where
      `foo` is the name of the dataset.
class_docstr_tok: ["Base","Dataset","with","directory","checker",".","Parameters","--","--","--","--","--","root",":","str","The","root","path","of","xxx.names",",","by","default","is","'~\/.mxnet\/datasets\/foo","'",",","where","`","foo","`","is","the","name","of","the","dataset","."]
code: def __init__(self, root):
      if not os.path.isdir(os.path.expanduser(root)):
          helper_msg = "{} is not a valid dir. Did you forget to initialize \
                           datasets described in: \
                           `https://cv.gluon.ai/build/examples_datasets/index.html`? \
                           You need to initialize each dataset only once.".format(
              root
          )
          raise OSError(helper_msg)
  
file_path: gluon-cv/gluoncv/data/base.py
imports: import os
  from mxnet.gluon.data import dataset
label_desc: Use image node_id 1 to create a new VisionDataset object from inherited base classes: dataset with example: obj = VisionDataset(root)