class_docstr: Defines a dataset for sequence tagging. Examples in this dataset
  contain paired lists -- paired list of words and tags.
  
  For example, in the case of part-of-speech tagging, an example is of the
  form
  [I, love, PyTorch, .] paired with [PRON, VERB, PROPN, PUNCT]
  
  See torchtext/test/sequence_tagging.py on how to use this class.
code: def sort_key(example):
      for attr in dir(example):
          if not callable(
              getattr(example, attr)
          ) and not attr.startswith("__"):
              return len(getattr(example, attr))
      return 0
  
file_path: pytext/pytext/legacy/datasets/sequence_tagging.py
imports: import random
  from ..None import data
label_desc: Use image node_id 1 for calling the SequenceTaggingDataset obj's underlying member method code with example usage: obj.sort_key(example) and returns: int, len