code: def __init__(
      self,
      root: str,
      transform: Optional[Callable] = None,
      target_transform: Optional[Callable] = None,
  ) -> None:
      import lmdb
  
      super().__init__(
          root, transform=transform, target_transform=target_transform
      )
  
      self.env = lmdb.open(
          root,
          max_readers=1,
          readonly=True,
          lock=False,
          readahead=False,
          meminit=False,
      )
      with self.env.begin(write=False) as txn:
          self.length = txn.stat()["entries"]
      cache_file = "_cache_" + "".join(
          c for c in root if c in string.ascii_letters
      )
      if os.path.isfile(cache_file):
          self.keys = pickle.load(open(cache_file, "rb"))
      else:
          with self.env.begin(write=False) as txn:
              self.keys = [
                  key
                  for key in txn.cursor().iternext(
                      keys=True, values=False
                  )
              ]
          pickle.dump(self.keys, open(cache_file, "wb"))
  
imports: import io
  import os.path
  import pickle
  import string
  from collections.abc import Iterable
  from typing import Any, Callable, cast, List, Optional, Tuple, Union
  from PIL import Image
  from .utils import iterable_to_str, verify_str_arg
  from .vision import VisionDataset
label_desc: Use image node_id 1 to create a new LSUNClass object from inherited base classes: VisionDataset with example: obj = LSUNClass(root, transform, target_transform)