Hook for logic before each handler starts.

def pre_handler(self, cmd):
        """Hook for logic before each handler starts."""
        if self._finished:
            return
        if self.interesting_commit and cmd.name == 'commit':
            if cmd.mark == self.interesting_commit:
                print(cmd.to_string())
                self._finished = True
            return
        if cmd.name in self.parsed_params:
            fields = self.parsed_params[cmd.name]
            str = cmd.dump_str(fields, self.parsed_params, self.verbose)
            print("%s" % (str,))