  provide methods for encoding/decoding strings in a list of token embeddings indices to be fed to a model.
All these classes can be instantiated from pretrained instances and saved locally using two methods:
from_pretrained() lets you instantiate a model/configuration/tokenizer from a pretrained version either
  provided by the library itself (the supported models can be found on the Model Hub) or
  stored locally (or on a server) by the user,
save_pretrained() lets you save a model/configuration/tokenizer locally so that it can be reloaded using
  from_pretrained().
