Open the GSR file located in the in self.outdir.
        Returns :class:`GsrFile` object, None if file could not be found or file is not readable.

def open_gsr(self):
        """
        Open the GSR file located in the in self.outdir.
        Returns :class:`GsrFile` object, None if file could not be found or file is not readable.
        """
        gsr_path = self.gsr_path
        if not gsr_path:
            if self.status == self.S_OK:
                logger.critical("%s reached S_OK but didn't produce a GSR file in %s" % (self, self.outdir))
            return None

        # Open the GSR file.
        from abipy.electrons.gsr import GsrFile
        try:
            return GsrFile(gsr_path)
        except Exception as exc:
            logger.critical("Exception while reading GSR file at %s:\n%s" % (gsr_path, str(exc)))
            return None