code: def open_hist(self):
          
          if not self.hist_path:
              if self.status == self.S_OK:
                  logger.critical("%s reached S_OK but didn't produce a HIST file in %s" % (self, self.outdir))
              return None
  
          # Open the HIST file
          from abipy.dynamics.hist import HistFile
          try:
              return HistFile(self.hist_path)
          except Exception as exc:
              logger.critical("Exception while reading HIST file at %s:\n%s" % (self.hist_path, str(exc)))
              return None
docs: Open the HIST file located in the in self.outdir.
          Returns :class:`HistFile` object, None if file could not be found or file is not readable.