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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add(self, work_dir, external=False):
 """Run a spooler on the specified directory. :param str|unicode work_dir: .. note:: Placeholders can be used to build paths, e.g.: {project_runtime_dir}/spool/ See ``Section.project_name`` and ``Section.runtime_dir``. :param bool external: map spoolers requests to a spooler directory managed by an external instance """

        command = 'spooler'

        if external:
            command += '-external'

        self._set(command, self._section.replace_placeholders(work_dir), multi=True)

        return self._section