docs: def _characterize_header(self, header, hgroups):
          """Characterize header groups into different data types.
          """
          out = []
          for h in [header[g[0]] for g in hgroups]:
              this_ctype = None
              for ctype, names in self._col_types.items():
                  if h.startswith(names):
                      this_ctype = ctype
                      break
              out.append(this_ctype)
          return out