Return raw files from source. Downloads/extracts if needed.

  Args:
    raw_dir: string directory to store raw files
    data_source: dictionary with
      {"url": url of compressed dataset containing input and target files
       "input": file with data in input language
       "target": file with data in target language}

  Returns:
    dictionary with
      {"inputs": list of files containing data in input language
       "targets": list of files containing corresponding data in target language
      }

def get_raw_files(raw_dir, data_source):
  """Return raw files from source. Downloads/extracts if needed.

  Args:
    raw_dir: string directory to store raw files
    data_source: dictionary with
      {"url": url of compressed dataset containing input and target files
       "input": file with data in input language
       "target": file with data in target language}

  Returns:
    dictionary with
      {"inputs": list of files containing data in input language
       "targets": list of files containing corresponding data in target language
      }
  """
  raw_files = {
      "inputs": [],
      "targets": [],
  }  # keys
  for d in data_source:
    input_file, target_file = download_and_extract(
        raw_dir, d["url"], d["input"], d["target"])
    raw_files["inputs"].append(input_file)
    raw_files["targets"].append(target_file)
  return raw_files