def abstract2sents(abstract, start, end):
  """Splits abstract text from datafile into list of sentences.

  Args:
    abstract: string containing <s> and </s> tags for starts and ends of sentences

  Returns:
    sents: List of sentence strings (no tags)"""
  cur = 0
  sents = []
  while True:
    try:
      start_p = abstract.index(start, cur)
      end_p = abstract.index(end, start_p + 1)
      cur = end_p + len(end)
      sents.append(abstract[start_p+len(start):end_p])
    except ValueError as e: # no more sentences

      return  ' '.join(sents)  # string