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.

def open_hist(self):
        """
        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.
        """
        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