docs: def _collapse_attributes(self, line, header, indexes):
          """Combine attributes in multiple columns into single named tuple.
          """
          names = []
          vals = []
          pat = re.compile("[\W]+")
          for i in indexes:
              names.append(pat.sub("_", self._clean_header(header[i])))
              vals.append(line[i])
          Attrs = collections.namedtuple('Attrs', names)
          return Attrs(*vals)