class_docstr: Version of fairseq.data.LanguagePairDataset which represents source
  sentences as sequences of words, each represented as a sequence of
  characters (with numberized indices for both words and characters).
  Right-padded only.
docstr: Length in words
docstr_tok: ["Length","in","words"]
code: def __len__(self):
      """Length in words"""
      return len(self.src)
  
imports: from typing import Any, Dict
  import numpy
  import torch
  from fairseq import data, tokenizer
  from fvcore.common.file_io import PathManager
  from pytorch_translate import vocab_constants
  from pytorch_translate.data.dictionary import TAGS
label_desc: Use image node_id 4 for calling the LanguagePairSourceCharDataset obj's underlying member method code with example usage: obj.__len__() and returns: len