code: def NCBISequenceLinkURL(title, default=None):
      
      try:
          ref = title.split('|')[3].split('.')[0]
      except IndexError:
          return default
      else:
          return 'http://www.ncbi.nlm.nih.gov/nuccore/%s' % (ref,)
docs: Given a sequence title, like "gi|42768646|gb|AY516849.1| Homo sapiens",
      return the URL of a link to the info page at NCBI.
  
      title: the sequence title to produce a link URL for.
      default: the value to return if the title cannot be parsed.