def _grab_history(self):
        """Calculate the needed history/changelog changes

        Every history heading looks like '1.0 b4 (1972-12-25)'. Extract them,
        check if the first one matches the version and whether it has a the
        current date.
        """
        default_location = None
        config = self.setup_cfg.config
        if config and config.has_option('zest.releaser', 'history_file'):
            default_location = config.get('zest.releaser', 'history_file')
        history_file = self.vcs.history_file(location=default_location)
        if not history_file:
            logger.warn("No history file found")
            self.data['history_lines'] = None
            self.data['history_file'] = None
            return
        logger.debug("Checking %s", history_file)
        history_lines = open(history_file).read().split('\n')
        # ^^^ TODO: .readlines()?
        headings = utils.extract_headings_from_history(history_lines)
        if not len(headings):
            logger.error("No detectable version heading in the history "
                         "file %s", history_file)
            sys.exit()
        good_heading = self.data['history_header'] % self.data
        # ^^^ history_header is a string with %(abc)s replacements.
        line = headings[0]['line']
        previous = history_lines[line]
        history_lines[line] = good_heading
        logger.debug("Set heading from %r to %r.", previous, good_heading)
        history_lines[line + 1] = utils.fix_rst_heading(
            heading=good_heading,
            below=history_lines[line + 1])
        logger.debug("Set line below heading to %r",
                     history_lines[line + 1])
        self.data['history_lines'] = history_lines
        self.data['history_file'] = history_file
Calculate the needed history/changelog changes

        Every history heading looks like '1.0 b4 (1972-12-25)'. Extract them,
        check if the first one matches the version and whether it has a the
        current date.