Write an executable file to the scripts directory

def write_script(self, script_name, contents, mode="t", blockers=()):
        """Write an executable file to the scripts directory"""
        self.delete_blockers(  # clean up old .py/.pyw w/o a script
            [os.path.join(self.script_dir, x) for x in blockers]
        )
        log.info("Installing %s script to %s", script_name, self.script_dir)
        target = os.path.join(self.script_dir, script_name)
        self.add_output(target)

        if self.dry_run:
            return

        mask = current_umask()
        ensure_directory(target)
        if os.path.exists(target):
            os.unlink(target)
        with open(target, "w" + mode) as f:
            f.write(contents)
        chmod(target, 0o777 - mask)