execute the pre script if it is defined

def pre_script(self):
        """
        execute the pre script if it is defined
        """
        if self['pre_script'] is None:
            return
        LOGGER.info("Executing pre script: {}".format(self['pre_script']))
        cmd = self['pre_script']
        execute_command(self.abs_input_dir(), cmd, self.env_dictionary())
        LOGGER.info("Pre Script completed")